|
I am a newbie Tek collector, having used my own 465 until some 20 years ago. I am reasonably knowledgeable in electronics.
The other day, I purchased a 7704 after only giving it a very quick test. I agree that wasn't very clever. Unfortunately I noticed some brightness and timebase issues and I decided to have a look inside the instrument. That wasn't very clever either...
I checked the +54.2 +- 0.25V without removing the power supply. It turned out OK (54.4). I decided to check some other voltages on the top regulator board and decided to remove the display unit (D7704) to reach in. I realized that many switching power supplies don't like very light loads but decided it was easier and the location of the description of how to remove the D7704 in the maintenance manual was such that I concluded it was safe. Also, I haven't found any warning re. this procedure.
Anyway, since I removed the D7704 and switched the PS on, there's a hissing sound from it and from what I measured, all preregulated voltages are much lower than normal: +54V now is 30V, -54V is -30V, 7V is 2V etc. Also, the front lights remain off (not surprising).
I'm anxious leaving the PS on for more than a few seconds.
My Question: Did I indeed blow up the PS and if so, is there a component that usually blows up and is the repair doable or even easy? There's no nasty burning smell or anything.
Or is this just a coincidence, and have I just witnessed another electrolytic capacitor dying?
Thanks for any ideas!
Raymond
|
You must be talking about the 7704A which is different from the 7704. The power supply needs the display unit to have minimum load. I usually measure what I can at the horizontal input connector.
Jerry Massengale
toggle quoted message
Show quoted text
-----Original Message-----
From: raymonddompfrank
To: TekScopes
Sent: Mon, May 21, 2012 8:20 pm
Subject: [TekScopes] 7704 power supply
?
I am a newbie Tek collector, having used my own 465 until some 20 years ago. I am reasonably knowledgeable in electronics.
The other day, I purchased a 7704 after only giving it a very quick test. I agree that wasn't very clever. Unfortunately I noticed some brightness and timebase issues and I decided to have a look inside the instrument. That wasn't very clever either...
I checked the +54.2 +- 0.25V without removing the power supply. It turned out OK (54.4). I decided to check some other voltages on the top regulator board and decided to remove the display unit (D7704) to reach in. I realized that many switching power supplies don't like very light loads but decided it was easier and the location of the description of how to remove the D7704 in the maintenance manual was such that I concluded it was safe. Also, I haven't found any warning re. this procedure.
Anyway, since I removed the D7704 and switched the PS on, there's a hissing sound from it and from what I measured, all preregulated voltages are much lower than normal: +54V now is 30V, -54V is -30V, 7V is 2V etc. Also, the front lights remain off (not surprising).
I'm anxious leaving the PS on for more than a few seconds.
My Question: Did I indeed blow up the PS and if so, is there a component that usually blows up and is the repair doable or even easy? There's no nasty burning smell or anything.
Or is this just a coincidence, and have I just witnessed another electrolytic capacitor dying?
Thanks for any ideas!
Raymond
|
Thanks for responding, Jerry. Of course, it's a 7704A, my bad.
Do you know if operating without Display Unit causes damage, did you ever do/try?
Raymond
toggle quoted message
Show quoted text
--- In TekScopes@..., jerry massengale <j_massengale@...> wrote:
You must be talking about the 7704A which is different from the 7704. The power supply needs the display unit to have minimum load. I usually measure what I can at the horizontal input connector.
Jerry Massengale
-----Original Message-----
From: raymonddompfrank <r.domp.frank@...>
To: TekScopes <TekScopes@...>
Sent: Mon, May 21, 2012 8:20 pm
Subject: [TekScopes] 7704 power supply
I am a newbie Tek collector, having used my own 465 until some 20 years ago. I am reasonably knowledgeable in electronics.
The other day, I purchased a 7704 after only giving it a very quick test. I agree that wasn't very clever. Unfortunately I noticed some brightness and timebase issues and I decided to have a look inside the instrument. That wasn't very clever either...
I checked the +54.2 +- 0.25V without removing the power supply. It turned out OK (54.4). I decided to check some other voltages on the top regulator board and decided to remove the display unit (D7704) to reach in. I realized that many switching power supplies don't like very light loads but decided it was easier and the location of the description of how to remove the D7704 in the maintenance manual was such that I concluded it was safe. Also, I haven't found any warning re. this procedure.
Anyway, since I removed the D7704 and switched the PS on, there's a hissing sound from it and from what I measured, all preregulated voltages are much lower than normal: +54V now is 30V, -54V is -30V, 7V is 2V etc. Also, the front lights remain off (not surprising).
I'm anxious leaving the PS on for more than a few seconds.
My Question: Did I indeed blow up the PS and if so, is there a component that usually blows up and is the repair doable or even easy? There's no nasty burning smell or anything.
Or is this just a coincidence, and have I just witnessed another electrolytic capacitor dying?
Thanks for any ideas!
Raymond
|
Hi,
I have tried it with just the bottom half but it never works. I have never damaged one by trying.
Jerry Massengale
toggle quoted message
Show quoted text
-----Original Message-----
From: raymonddompfrank
To: TekScopes <TekScopes@...>
Sent: Mon, May 21, 2012 9:40 pm
Subject: [TekScopes] Re: 7704 power supply
?
Thanks for responding, Jerry. Of course, it's a 7704A, my bad.
Do you know if operating without Display Unit causes damage, did you ever do/try?
Raymond
--- In TekScopes@..., jerry massengale wrote:
>
> You must be talking about the 7704A which is different from the 7704. The power supply needs the display unit to have minimum load. I usually measure what I can at the horizontal input connector.
>
>
> Jerry Massengale
>
>
>
>
>
> -----Original Message-----
> From: raymonddompfrank
> To: TekScopes < TekScopes@...>
> Sent: Mon, May 21, 2012 8:20 pm
> Subject: [TekScopes] 7704 power supply
>
>
>
>
>
> I am a newbie Tek collector, having used my own 465 until some 20 years ago. I am reasonably knowledgeable in electronics.
>
> The other day, I purchased a 7704 after only giving it a very quick test. I agree that wasn't very clever. Unfortunately I noticed some brightness and timebase issues and I decided to have a look inside the instrument. That wasn't very clever either...
> I checked the +54.2 +- 0.25V without removing the power supply. It turned out OK (54.4). I decided to check some other voltages on the top regulator board and decided to remove the display unit (D7704) to reach in. I realized that many switching power supplies don't like very light loads but decided it was easier and the location of the description of how to remove the D7704 in the maintenance manual was such that I concluded it was safe. Also, I haven't found any warning re. this procedure.
> Anyway, since I removed the D7704 and switched the PS on, there's a hissing sound from it and from what I measured, all preregulated voltages are much lower than normal: +54V now is 30V, -54V is -30V, 7V is 2V etc. Also, the front lights remain off (not surprising).
> I'm anxious leaving the PS on for more than a few seconds.
>
> My Question: Did I indeed blow up the PS and if so, is there a component that usually blows up and is the repair doable or even easy? There's no nasty burning smell or anything.
> Or is this just a coincidence, and have I just witnessed another electrolytic capacitor dying?
>
> Thanks for any ideas!
>
> Raymond
>
|
Raymond,
I have repared my 7704A two times. Be sure to have the right manual. Most manuals are about the 7704 and that has no switching power supply.
The powersupply will not start without a load but it keeps trying.
I removed the psu and then connected it outside the mainframe. If there is. Problem on the rails most chances are bad caps. I had to replace to electrolitics and two tantaliums. Both rather small filtercaps. Problem is tht it is hard to get acces fr measuring while powered on.
My problem was trace compression just after starting it up.
The second problem was an easy fix, again trace compresion but this time permanent. The problem was a dirty pot on the X amp on top of the CRT, that distrorted the sawtooth. They are very nice scopes but also complex.
A hiss and penetrant smell are typical for a cooking electrolyte. I becomes hot and builds up pressure in side. Modern caps have a top that pops open, so they are easy to spot, old caps blow there guts to the underside.
Connect your psu outside the mainframe but in such a way it is connected. I can not remember if i used a sort of extension lead, sorry bit my memory is very bad.
Then measure ripple and voltages. The psu is comlicated but explained in the manual. Much rils depends on each other, so if one rail is wrong, search in that rail, if more are wrong the problem is probably one common level under that. Your scope worked so the psu can not be terrible bad. If it is not used fr many years and fired up after that the caps have. Hard time. If you are lucky they reform. If not they start leaking DC and cook dry.
If the rails are OK, check the HV testpoint. If there is a problem there you have most times problems with intensity and focus.
Good luck, hope you can fix it, it is a great scope.
Fred pa4tim
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Show quoted text
--- In TekScopes@..., jerry massengale <j_massengale@...> wrote:
You must be talking about the 7704A which is different from the 7704. The power supply needs the display unit to have minimum load. I usually measure what I can at the horizontal input connector.
Jerry Massengale
-----Original Message-----
From: raymonddompfrank <r.domp.frank@...>
To: TekScopes <TekScopes@...>
Sent: Mon, May 21, 2012 8:20 pm
Subject: [TekScopes] 7704 power supply
I am a newbie Tek collector, having used my own 465 until some 20 years ago. I am reasonably knowledgeable in electronics.
The other day, I purchased a 7704 after only giving it a very quick test. I agree that wasn't very clever. Unfortunately I noticed some brightness and timebase issues and I decided to have a look inside the instrument. That wasn't very clever either...
I checked the +54.2 +- 0.25V without removing the power supply. It turned out OK (54.4). I decided to check some other voltages on the top regulator board and decided to remove the display unit (D7704) to reach in. I realized that many switching power supplies don't like very light loads but decided it was easier and the location of the description of how to remove the D7704 in the maintenance manual was such that I concluded it was safe. Also, I haven't found any warning re. this procedure.
Anyway, since I removed the D7704 and switched the PS on, there's a hissing sound from it and from what I measured, all preregulated voltages are much lower than normal: +54V now is 30V, -54V is -30V, 7V is 2V etc. Also, the front lights remain off (not surprising).
I'm anxious leaving the PS on for more than a few seconds.
My Question: Did I indeed blow up the PS and if so, is there a component that usually blows up and is the repair doable or even easy? There's no nasty burning smell or anything.
Or is this just a coincidence, and have I just witnessed another electrolytic capacitor dying?
Thanks for any ideas!
Raymond
|
*Now* I know what it sounds like but couldn't think of: It's like an ultrasonic cleaner, though not as loud and not quite as steady volume-wise.
Raymond
toggle quoted message
Show quoted text
--- In TekScopes@..., "raymonddompfrank" <r.domp.frank@...> wrote:
I am a newbie Tek collector, having used my own 465 until some 20 years ago. I am reasonably knowledgeable in electronics.
The other day, I purchased a 7704 after only giving it a very quick test. I agree that wasn't very clever. Unfortunately I noticed some brightness and timebase issues and I decided to have a look inside the instrument. That wasn't very clever either...
I checked the +54.2 +- 0.25V without removing the power supply. It turned out OK (54.4). I decided to check some other voltages on the top regulator board and decided to remove the display unit (D7704) to reach in. I realized that many switching power supplies don't like very light loads but decided it was easier and the location of the description of how to remove the D7704 in the maintenance manual was such that I concluded it was safe. Also, I haven't found any warning re. this procedure.
Anyway, since I removed the D7704 and switched the PS on, there's a hissing sound from it and from what I measured, all preregulated voltages are much lower than normal: +54V now is 30V, -54V is -30V, 7V is 2V etc. Also, the front lights remain off (not surprising).
I'm anxious leaving the PS on for more than a few seconds.
My Question: Did I indeed blow up the PS and if so, is there a component that usually blows up and is the repair doable or even easy? There's no nasty burning smell or anything.
Or is this just a coincidence, and have I just witnessed another electrolytic capacitor dying?
Thanks for any ideas!
Raymond
|
?
Hi Raymond,
I think some component turned bad when you exercised the scope. It may have been stored unused for a long time.
It can be a cap or diode, we don’t know yet. You have come this far which is a good start. You can repair it, sure, but it requires some serious thinking first.
Most likely there is only one bad component. You need to find out if any of the regulated outputs (+50, +15, +5 etc.)
Is overloaded. Is it possible to disconnect one output at a time and see what happens? Be careful.
?
?
Good luck
G?ran
?
?
|
Hi Raymond,
Another scenario is that you created an Accelerated Life Test by taking off the D-unit. The overvoltage protection will repeatedly switch off the PS, but at a several percent higher voltage than normal. If some cap wanted to die then this was the moment! This only concerns the LV filter caps. Like Fred said, a cap can make that hissing sound. Sometimes a cap starts to leak dramatically above a certain voltage (I have seen that in a 7704A, IIRC including hissing).
What I understand is that the LVs are bad now even with the D-unit reinstalled. First thing is to throw away your DMM: why do you have a 7844? Probe the pre-regulated voltages (+/- 54V, +/- 17V, +7V) at the LV board (with or without D-unit). You will recognize the start attempts of the PS. With some luck you might find one off those voltages to collapse much faster than the others -- likely due to the failing cap then.
Albert
toggle quoted message
Show quoted text
Hi Raymond,
I think some component turned bad when you exercised the scope. It may have been stored unused for a long time.
It can be a cap or diode, we don't know yet. You have come this far which is a good start. You can repair it, sure, but it requires some serious thinking first.
Most likely there is only one bad component. You need to find out if any of the regulated outputs (+50, +15, +5 etc.)
Is overloaded. Is it possible to disconnect one output at a time and see what happens? Be careful.
Good luck
G?ran
|
|
|
Wanting to avoid too long a message, I didn't mention that I "lost" that 465 in 1994 when I sold my company.
However:
In recent weeks I have purchased a 465B in excellent condition, without the rubber feet (disintegrated, anyone knows where to get those?), an R7844 in excellent condition, a mostly non-functional 2445B (since repaired) and ... a 7704A, now repaired!
It turned out that one bridge rectifier diode (CR3182) on the inverter/rectifier board had short-circuited.
I replaced it with a diode (1N5406) from a broken Apple PowerMac G5 computer. I guess it'll do the job OK. The circuit is just supplying 5V for the indicator lights.
Reason I used a DMM is, the maintenance manual states that the pre-regulator +54V should be 54.2 +- 0.25 V. I don't understand why it should be within 0,5% but it's certainly easier to measure with a DMM than with a scope...
Now I only have to correct the brightness/focus isssue...
Raymond
Raymond
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Show quoted text
--- In TekScopes@..., "Albert" <aodiversen@...> wrote:
Actually you said a 465.
Albert
First thing is to throw away your DMM: why do you have a 7844?
|
Hello guys,
I have been able to repair my 7704A! It turned out that one bridge rectifier diode (CR3182) on the inverter/rectifier board was shorted, causing a periodic short-circuit in transformer T3101. It was the transformer making the noise. I used a 1N5406 from a broken Apple PowerMac G5 as a replacement.
I can't understand why it broke down the moment when I first switched the PS on without the load of the display unit (D7704).
Thank you all very much for your help, hints and encouraging words.
This forum has certainly been good to me with my first posting!
Next, I'll try and resolve the brightness/focus issue.
Best regards,
Raymond
toggle quoted message
Show quoted text
--- In TekScopes@..., "raymonddompfrank" <r.domp.frank@...> wrote:
I am a newbie Tek collector, having used my own 465 until some 20 years ago. I am reasonably knowledgeable in electronics.
The other day, I purchased a 7704 after only giving it a very quick test. I agree that wasn't very clever. Unfortunately I noticed some brightness and timebase issues and I decided to have a look inside the instrument. That wasn't very clever either...
I checked the +54.2 +- 0.25V without removing the power supply. It turned out OK (54.4). I decided to check some other voltages on the top regulator board and decided to remove the display unit (D7704) to reach in. I realized that many switching power supplies don't like very light loads but decided it was easier and the location of the description of how to remove the D7704 in the maintenance manual was such that I concluded it was safe. Also, I haven't found any warning re. this procedure.
Anyway, since I removed the D7704 and switched the PS on, there's a hissing sound from it and from what I measured, all preregulated voltages are much lower than normal: +54V now is 30V, -54V is -30V, 7V is 2V etc. Also, the front lights remain off (not surprising).
I'm anxious leaving the PS on for more than a few seconds.
My Question: Did I indeed blow up the PS and if so, is there a component that usually blows up and is the repair doable or even easy? There's no nasty burning smell or anything.
Or is this just a coincidence, and have I just witnessed another electrolytic capacitor dying?
Thanks for any ideas!
Raymond
|
Hi Raymond, In recent weeks I have purchased a 465B in excellent condition, without the rubber feet (disintegrated, anyone knows where to get those?), an R7844 in excellent condition, a mostly non-functional 2445B (since repaired) and ... a 7704A, now repaired! You will soon need a larger shack if you continue collecting that fast :=). It turned out that one bridge rectifier diode (CR3182) on the inverter/rectifier board had short-circuited. Congratulations that you found the fault so quickly! Reason I used a DMM is, the maintenance manual states that the pre-regulator +54V should be 54.2 +- 0.25 V. I don't understand why it should be within 0,5% but it's certainly easier to measure with a DMM than with a scope...
---
Raymond It's a calibration requirement that will guarantee that some other requirements will be met or within adjustment range. Specifically the HV circuits. Of course there will have been many design considerations to arrive at all those voltages. A 'scope comes in when the voltage is abnormal and likely not pure DC. I once had the LV reference voltage slightly off, not well adjustable and instable. First thought was a bad adjustment pot. Probing with a 'scope revealed that there was oscillation in the circuit (due to a bad Main Interface board cap). Albert
|
Hi Raymond,
A question about your diode substitution.
What frequency does that diode run at in the
7704A?
And is?the 1N5406?suitable for?that
frequency?
The data sheet for 1N5406 makes?me think?it is only
good for low frequencies.
I don't have a 7704A manual handy to answer my own
question.
tom jobe...
?
?
?
toggle quoted message
Show quoted text
----- Original Message -----
Sent: Tuesday, May 22, 2012 12:47
PM
Subject: [TekScopes] Re: 7704 power
supply
?
Hello guys,
I have been able to repair my 7704A! It turned out
that one bridge rectifier diode (CR3182) on the inverter/rectifier board was
shorted, causing a periodic short-circuit in transformer T3101. It was the
transformer making the noise. I used a 1N5406 from a broken Apple PowerMac G5
as a replacement.
I can't understand why it broke down the moment when I
first switched the PS on without the load of the display unit
(D7704).
Thank you all very much for your help, hints and encouraging
words.
This forum has certainly been good to me with my first
posting!
Next, I'll try and resolve the brightness/focus
issue.
Best regards,
Raymond
--- In TekScopes@...,
"raymonddompfrank" <r.domp.frank@...> wrote:
>
> I am a
newbie Tek collector, having used my own 465 until some 20 years ago. I am
reasonably knowledgeable in electronics.
>
> The other day, I
purchased a 7704 after only giving it a very quick test. I agree that wasn't
very clever. Unfortunately I noticed some brightness and timebase issues and I
decided to have a look inside the instrument. That wasn't very clever
either...
> I checked the +54.2 +- 0.25V without removing the power
supply. It turned out OK (54.4). I decided to check some other voltages on the
top regulator board and decided to remove the display unit (D7704) to reach
in. I realized that many switching power supplies don't like very light loads
but decided it was easier and the location of the description of how to remove
the D7704 in the maintenance manual was such that I concluded it was safe.
Also, I haven't found any warning re. this procedure.
> Anyway, since I
removed the D7704 and switched the PS on, there's a hissing sound from it and
from what I measured, all preregulated voltages are much lower than normal:
+54V now is 30V, -54V is -30V, 7V is 2V etc. Also, the front lights remain off
(not surprising).
> I'm anxious leaving the PS on for more than a few
seconds.
>
> My Question: Did I indeed blow up the PS and if so,
is there a component that usually blows up and is the repair doable or even
easy? There's no nasty burning smell or anything.
> Or is this just a
coincidence, and have I just witnessed another electrolytic capacitor
dying?
>
> Thanks for any ideas!
>
>
Raymond
>
|
Hi Tom,
Thanks for thinking for me! I hadn't given this even a moment's thought! Obviously, my electronic alertness is a bit off after having been out of it for around 20 years...
You're right about the 1N5406, it's a "standard recovery" diode. The circuit runs at around 50KHz. I don't know the characteristics of these diodes at this frequency. The SMPS doesn't see it as a shortcut though...
It's one of 2 diodes in a half-bridge, supplying 5V to ... the light bulbs only, through a CLC-filter.
The load on the transformer may be another matter. I'll try and find a way to access some measuring points while the scope is switched on or at least I'll watch for effects that may be caused by this.
Thanks again for this!
Raymond
toggle quoted message
Show quoted text
--- In TekScopes@..., "Tom Jobe" <tomjobe@...> wrote:
Hi Raymond,
A question about your diode substitution.
What frequency does that diode run at in the 7704A?
And is the 1N5406 suitable for that frequency?
The data sheet for 1N5406 makes me think it is only good for low frequencies.
I don't have a 7704A manual handy to answer my own question.
tom jobe...
----- Original Message -----
From: raymonddompfrank
To: TekScopes@...
Sent: Tuesday, May 22, 2012 12:47 PM
Subject: [TekScopes] Re: 7704 power supply
Hello guys,
I have been able to repair my 7704A! It turned out that one bridge rectifier diode (CR3182) on the inverter/rectifier board was shorted, causing a periodic short-circuit in transformer T3101. It was the transformer making the noise. I used a 1N5406 from a broken Apple PowerMac G5 as a replacement.
I can't understand why it broke down the moment when I first switched the PS on without the load of the display unit (D7704).
Thank you all very much for your help, hints and encouraging words.
This forum has certainly been good to me with my first posting!
Next, I'll try and resolve the brightness/focus issue.
Best regards,
Raymond
--- In TekScopes@..., "raymonddompfrank" <r.domp.frank@> wrote:
>
> I am a newbie Tek collector, having used my own 465 until some 20 years ago. I am reasonably knowledgeable in electronics.
>
> The other day, I purchased a 7704 after only giving it a very quick test. I agree that wasn't very clever. Unfortunately I noticed some brightness and timebase issues and I decided to have a look inside the instrument. That wasn't very clever either...
> I checked the +54.2 +- 0.25V without removing the power supply. It turned out OK (54.4). I decided to check some other voltages on the top regulator board and decided to remove the display unit (D7704) to reach in. I realized that many switching power supplies don't like very light loads but decided it was easier and the location of the description of how to remove the D7704 in the maintenance manual was such that I concluded it was safe. Also, I haven't found any warning re. this procedure.
> Anyway, since I removed the D7704 and switched the PS on, there's a hissing sound from it and from what I measured, all preregulated voltages are much lower than normal: +54V now is 30V, -54V is -30V, 7V is 2V etc. Also, the front lights remain off (not surprising).
> I'm anxious leaving the PS on for more than a few seconds.
>
> My Question: Did I indeed blow up the PS and if so, is there a component that usually blows up and is the repair doable or even easy? There's no nasty burning smell or anything.
> Or is this just a coincidence, and have I just witnessed another electrolytic capacitor dying?
>
> Thanks for any ideas!
>
> Raymond
>
|
--- In TekScopes@..., "Albert" <aodiversen@...> wrote:
Hi Raymond,
In recent weeks I have purchased a 465B in excellent condition, without the rubber feet (disintegrated, anyone knows where to get those?), an R7844 in excellent condition, a mostly non-functional 2445B (since repaired) and ... a 7704A, now repaired! You will soon need a larger shack if you continue collecting that fast :=).
It turned out that one bridge rectifier diode (CR3182) on the inverter/rectifier board had short-circuited. Congratulations that you found the fault so quickly!
Reason I used a DMM is, the maintenance manual states that the pre-regulator +54V should be 54.2 +- 0.25 V. I don't understand why it should be within 0,5% but it's certainly easier to measure with a DMM than with a scope...
---
Raymond It's a calibration requirement that will guarantee that some other requirements will be met or within adjustment range. Specifically the HV circuits. Of course there will have been many design considerations to arrive at all those voltages.
A 'scope comes in when the voltage is abnormal and likely not pure DC. I once had the LV reference voltage slightly off, not well adjustable and instable. First thought was a bad adjustment pot. Probing with a 'scope revealed that there was oscillation in the circuit (due to a bad Main Interface board cap).
Albert
Thanks for your insight, Albert.
|
Hi Raymond,
Today I found a 7704A service manual, and it says that CR3182
is a 1N5823 which is a 5 amp Schottky diode.
You might want to do some diode shopping soon.
tom jobe...
?
?
?
toggle quoted message
Show quoted text
----- Original Message -----
Sent: Tuesday, May 22, 2012 5:57 PM
Subject: [TekScopes] Re: 7704 power
supply
?
Hi Tom,
Thanks for thinking for me! I hadn't given this even a moment's
thought! Obviously, my electronic alertness is a bit off after having been out
of it for around 20 years...
You're right about the 1N5406, it's a
"standard recovery" diode. The circuit runs at around 50KHz. I don't know the
characteristics of these diodes at this frequency. The SMPS doesn't see it as
a shortcut though...
It's one of 2 diodes in a half-bridge, supplying 5V to
... the light bulbs only, through a CLC-filter.
The load on the
transformer may be another matter. I'll try and find a way to access some
measuring points while the scope is switched on or at least I'll watch for
effects that may be caused by this.
Thanks again for
this!
Raymond
--- In TekScopes@..., "Tom
Jobe" wrote:
>
> Hi Raymond,
> A
question about your diode substitution.
> What frequency does that diode
run at in the 7704A?
> And is the 1N5406 suitable for that
frequency?
> The data sheet for 1N5406 makes me think it is only good
for low frequencies.
> I don't have a 7704A manual handy to answer my
own question.
> tom jobe...
>
>
>
> -----
Original Message -----
> From: raymonddompfrank
> To: TekScopes@...
> Sent: Tuesday, May 22, 2012 12:47 PM
> Subject: [TekScopes] Re:
7704 power supply
>
>
>
>
>
> Hello
guys,
> I have been able to repair my 7704A! It turned out that one
bridge rectifier diode (CR3182) on the inverter/rectifier board was shorted,
causing a periodic short-circuit in transformer T3101. It was the transformer
making the noise. I used a 1N5406 from a broken Apple PowerMac G5 as a
replacement.
> I can't understand why it broke down the moment when I
first switched the PS on without the load of the display unit (D7704).
>
> Thank you all very much for your help, hints and encouraging
words.
> This forum has certainly been good to me with my first
posting!
>
> Next, I'll try and resolve the brightness/focus
issue.
>
> Best regards,
>
> Raymond
>
> --- In TekScopes@...,
"raymonddompfrank" wrote:
> >
> > I am
a newbie Tek collector, having used my own 465 until some 20 years ago. I am
reasonably knowledgeable in electronics.
> >
> > The other
day, I purchased a 7704 after only giving it a very quick test. I agree that
wasn't very clever. Unfortunately I noticed some brightness and timebase
issues and I decided to have a look inside the instrument. That wasn't very
clever either...
> > I checked the +54.2 +- 0.25V without removing
the power supply. It turned out OK (54.4). I decided to check some other
voltages on the top regulator board and decided to remove the display unit
(D7704) to reach in. I realized that many switching power supplies don't like
very light loads but decided it was easier and the location of the description
of how to remove the D7704 in the maintenance manual was such that I concluded
it was safe. Also, I haven't found any warning re. this procedure.
>
> Anyway, since I removed the D7704 and switched the PS on, there's a
hissing sound from it and from what I measured, all preregulated voltages are
much lower than normal: +54V now is 30V, -54V is -30V, 7V is 2V etc. Also, the
front lights remain off (not surprising).
> > I'm anxious leaving the
PS on for more than a few seconds.
> >
> > My Question: Did
I indeed blow up the PS and if so, is there a component that usually blows up
and is the repair doable or even easy? There's no nasty burning smell or
anything.
> > Or is this just a coincidence, and have I just
witnessed another electrolytic capacitor dying?
> >
> >
Thanks for any ideas!
> >
> > Raymond
>
>
>
|
Tom,
It turns out that the original diode is a 20V 5A Schottky, 1N5823...
Do you think 50KHz is too high for the 1N5406, taking the noncritical place into consideration?
toggle quoted message
Show quoted text
--- In TekScopes@..., "raymonddompfrank" <r.domp.frank@...> wrote:
Hi Tom,
Thanks for thinking for me! I hadn't given this even a moment's thought! Obviously, my electronic alertness is a bit off after having been out of it for around 20 years...
You're right about the 1N5406, it's a "standard recovery" diode. The circuit runs at around 50KHz. I don't know the characteristics of these diodes at this frequency. The SMPS doesn't see it as a shortcut though...
It's one of 2 diodes in a half-bridge, supplying 5V to ... the light bulbs only, through a CLC-filter.
The load on the transformer may be another matter. I'll try and find a way to access some measuring points while the scope is switched on or at least I'll watch for effects that may be caused by this.
Thanks again for this!
Raymond
--- In TekScopes@..., "Tom Jobe" <tomjobe@> wrote:
Hi Raymond,
A question about your diode substitution.
What frequency does that diode run at in the 7704A?
And is the 1N5406 suitable for that frequency?
The data sheet for 1N5406 makes me think it is only good for low frequencies.
I don't have a 7704A manual handy to answer my own question.
tom jobe...
----- Original Message -----
From: raymonddompfrank
To: TekScopes@...
Sent: Tuesday, May 22, 2012 12:47 PM
Subject: [TekScopes] Re: 7704 power supply
Hello guys,
I have been able to repair my 7704A! It turned out that one bridge rectifier diode (CR3182) on the inverter/rectifier board was shorted, causing a periodic short-circuit in transformer T3101. It was the transformer making the noise. I used a 1N5406 from a broken Apple PowerMac G5 as a replacement.
I can't understand why it broke down the moment when I first switched the PS on without the load of the display unit (D7704).
Thank you all very much for your help, hints and encouraging words.
This forum has certainly been good to me with my first posting!
Next, I'll try and resolve the brightness/focus issue.
Best regards,
Raymond
--- In TekScopes@..., "raymonddompfrank" <r.domp.frank@> wrote:
>
> I am a newbie Tek collector, having used my own 465 until some 20 years ago. I am reasonably knowledgeable in electronics.
>
> The other day, I purchased a 7704 after only giving it a very quick test. I agree that wasn't very clever. Unfortunately I noticed some brightness and timebase issues and I decided to have a look inside the instrument. That wasn't very clever either...
> I checked the +54.2 +- 0.25V without removing the power supply. It turned out OK (54.4). I decided to check some other voltages on the top regulator board and decided to remove the display unit (D7704) to reach in. I realized that many switching power supplies don't like very light loads but decided it was easier and the location of the description of how to remove the D7704 in the maintenance manual was such that I concluded it was safe. Also, I haven't found any warning re. this procedure.
> Anyway, since I removed the D7704 and switched the PS on, there's a hissing sound from it and from what I measured, all preregulated voltages are much lower than normal: +54V now is 30V, -54V is -30V, 7V is 2V etc. Also, the front lights remain off (not surprising).
> I'm anxious leaving the PS on for more than a few seconds.
>
> My Question: Did I indeed blow up the PS and if so, is there a component that usually blows up and is the repair doable or even easy? There's no nasty burning smell or anything.
> Or is this just a coincidence, and have I just witnessed another electrolytic capacitor dying?
>
> Thanks for any ideas!
>
> Raymond
>
|
Hi Tom,
Our messages crossed, will go shopping!
toggle quoted message
Show quoted text
--- In TekScopes@..., "Tom Jobe" <tomjobe@...> wrote:
Hi Raymond,
Today I found a 7704A service manual, and it says that CR3182 is a 1N5823 which is a 5 amp Schottky diode.
You might want to do some diode shopping soon.
tom jobe...
----- Original Message -----
From: raymonddompfrank
To: TekScopes@...
Sent: Tuesday, May 22, 2012 5:57 PM
Subject: [TekScopes] Re: 7704 power supply
Hi Tom,
Thanks for thinking for me! I hadn't given this even a moment's thought! Obviously, my electronic alertness is a bit off after having been out of it for around 20 years...
You're right about the 1N5406, it's a "standard recovery" diode. The circuit runs at around 50KHz. I don't know the characteristics of these diodes at this frequency. The SMPS doesn't see it as a shortcut though...
It's one of 2 diodes in a half-bridge, supplying 5V to ... the light bulbs only, through a CLC-filter.
The load on the transformer may be another matter. I'll try and find a way to access some measuring points while the scope is switched on or at least I'll watch for effects that may be caused by this.
Thanks again for this!
Raymond
--- In TekScopes@..., "Tom Jobe" <tomjobe@> wrote:
>
> Hi Raymond,
> A question about your diode substitution.
> What frequency does that diode run at in the 7704A?
> And is the 1N5406 suitable for that frequency?
> The data sheet for 1N5406 makes me think it is only good for low frequencies.
> I don't have a 7704A manual handy to answer my own question.
> tom jobe...
>
>
>
> ----- Original Message -----
> From: raymonddompfrank
> To: TekScopes@...
> Sent: Tuesday, May 22, 2012 12:47 PM
> Subject: [TekScopes] Re: 7704 power supply
>
>
>
>
>
> Hello guys,
> I have been able to repair my 7704A! It turned out that one bridge rectifier diode (CR3182) on the inverter/rectifier board was shorted, causing a periodic short-circuit in transformer T3101. It was the transformer making the noise. I used a 1N5406 from a broken Apple PowerMac G5 as a replacement.
> I can't understand why it broke down the moment when I first switched the PS on without the load of the display unit (D7704).
>
> Thank you all very much for your help, hints and encouraging words.
> This forum has certainly been good to me with my first posting!
>
> Next, I'll try and resolve the brightness/focus issue.
>
> Best regards,
>
> Raymond
>
> --- In TekScopes@..., "raymonddompfrank" <r.domp.frank@> wrote:
> >
> > I am a newbie Tek collector, having used my own 465 until some 20 years ago. I am reasonably knowledgeable in electronics.
> >
> > The other day, I purchased a 7704 after only giving it a very quick test. I agree that wasn't very clever. Unfortunately I noticed some brightness and timebase issues and I decided to have a look inside the instrument. That wasn't very clever either...
> > I checked the +54.2 +- 0.25V without removing the power supply. It turned out OK (54.4). I decided to check some other voltages on the top regulator board and decided to remove the display unit (D7704) to reach in. I realized that many switching power supplies don't like very light loads but decided it was easier and the location of the description of how to remove the D7704 in the maintenance manual was such that I concluded it was safe. Also, I haven't found any warning re. this procedure.
> > Anyway, since I removed the D7704 and switched the PS on, there's a hissing sound from it and from what I measured, all preregulated voltages are much lower than normal: +54V now is 30V, -54V is -30V, 7V is 2V etc. Also, the front lights remain off (not surprising).
> > I'm anxious leaving the PS on for more than a few seconds.
> >
> > My Question: Did I indeed blow up the PS and if so, is there a component that usually blows up and is the repair doable or even easy? There's no nasty burning smell or anything.
> > Or is this just a coincidence, and have I just witnessed another electrolytic capacitor dying?
> >
> > Thanks for any ideas!
> >
> > Raymond
> >
>
|
Hi Raymond,
When I bought my 465 it also had the disintegrating rubber feet.?
Since they are also used as cable wrap I wanted to replace them and
found a set NOS from a reputable seller.? I bought them but they
began to also disintegrate within days.? They were really new, in an
original Tek bag, but it seems that the rubber deteriorates with
time so probably all the feet that you find, either used or new,
will also disintegrate.? Anyway YMMV (Is it the correct spelling?).
Regards,
Ignacio, EB4APL
On 22/05/2012 21:31, raymonddompfrank wrote:
toggle quoted message
Show quoted text
?
Wanting to avoid too long a message, I didn't mention that
I "lost" that 465 in 1994 when I sold my company.
However:
In recent weeks I have purchased a 465B in excellent
condition, without the rubber feet (disintegrated, anyone
knows where to get those?), an R7844 in excellent
condition, a mostly non-functional 2445B (since repaired)
and ... a 7704A, now repaired!
It turned out that one bridge rectifier diode (CR3182) on
the inverter/rectifier board had short-circuited.
I replaced it with a diode (1N5406) from a broken Apple
PowerMac G5 computer. I guess it'll do the job OK. The
circuit is just supplying 5V for the indicator lights.
Reason I used a DMM is, the maintenance manual states that
the pre-regulator +54V should be 54.2 +- 0.25 V. I don't
understand why it should be within 0,5% but it's certainly
easier to measure with a DMM than with a scope...
Now I only have to correct the brightness/focus isssue...
Raymond
Raymond
--- In TekScopes@...,
"Albert" wrote:
>
> Actually you said a 465.
> Albert
>
> > First thing is to throw away your DMM: why do
you have a 7844?
>
|
Having been through the 4xx crumbling rear foot problem
several times, I made up some replacement feet out of plastic bar
stock.
Attached are some pictures of these new feet. The power cord
wraps around them just like the originals.
I have no interest in making any of these feet?for
anyone, but I will offer to make a simple dimensioned sketch if anyone wants
it.
tom jobe...
?
?
?
toggle quoted message
Show quoted text
----- Original Message -----
Sent: Tuesday, May 22, 2012 6:33 PM
Subject: Re: [TekScopes] Re: 7704 power
supply
?
Hi Raymond,
When I bought my 465 it also had the disintegrating
rubber feet.? Since they are also used as cable wrap I wanted to replace
them and found a set NOS from a reputable seller.? I bought them but they
began to also disintegrate within days.? They were really new, in an
original Tek bag, but it seems that the rubber deteriorates with time so
probably all the feet that you find, either used or new, will also
disintegrate.? Anyway YMMV (Is it the correct
spelling?).
Regards,
Ignacio, EB4APL
On 22/05/2012 21:31,
raymonddompfrank wrote:
?
Wanting to avoid too long a message, I didn't mention that I "lost"
that 465 in 1994 when I sold my company.
However:
In recent weeks I
have purchased a 465B in excellent condition, without the rubber feet
(disintegrated, anyone knows where to get those?), an R7844 in excellent
condition, a mostly non-functional 2445B (since repaired) and ... a 7704A,
now repaired!
It turned out that one bridge rectifier diode (CR3182) on
the inverter/rectifier board had short-circuited.
I replaced it with a
diode (1N5406) from a broken Apple PowerMac G5 computer. I guess it'll do
the job OK. The circuit is just supplying 5V for the indicator
lights.
Reason I used a DMM is, the maintenance manual states that
the pre-regulator +54V should be 54.2 +- 0.25 V. I don't understand why it
should be within 0,5% but it's certainly easier to measure with a DMM than
with a scope...
Now I only have to correct the brightness/focus
isssue...
Raymond
Raymond
--- In TekScopes@..., "Albert"
wrote:
>
> Actually you said a 465.
> Albert
>
> > First thing is to throw away your DMM: why do you have a
7844?
>
|
