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Magnus,
I just pulled it out. IT IS OPEN!
I will replace it now. Yes, I was not getting any PWM, so I was thinking it wasn't oscillating.? I will let?you know. Many thanks so far!
Thank you!
Bill
Bill
[Edited Message Follows]
I had a similar issue with my 8920B. In my case it was a resistor that went open circuit, without any sign of burns or high temperature. Unfortunately I cant remember where i found the information about this so I just write what I remember.
The resistor should have a value like 1 Mohm and serve as some kind of kickstart for the switching circuits. It also serves as a bleeder for the main "bucket" capacitor, so this will remain charged at a high voltage level for a long time! Be aware! And two of the heat sinks are connected to each side of the capacitor so you might have up to 400V between these! Be aware!! :-)
While writing this and looking for more information i stumble over this video
With links to schematics for the power supply. According to these it might have been R3 (470k) that were open circuit in my HP8920B.
/Magnus, SM7UGO
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Thank you very much! I will check. I am here in Wall twp, NJ. I decided tonight to take a break. I know about the high voltage.? Thankyou! I just noticed the email or I would have replied much sooner. I will let?you know.?
Bill DiCarlo?
[Edited Message Follows]
I had a similar issue with my 8920B. In my case it was a resistor that went open circuit, without any sign of burns or high temperature. Unfortunately I cant remember where i found the information about this so I just write what I remember.
The resistor should have a value like 1 Mohm and serve as some kind of kickstart for the switching circuits. It also serves as a bleeder for the main "bucket" capacitor, so this will remain charged at a high voltage level for a long time! Be aware! And two of the heat sinks are connected to each side of the capacitor so you might have up to 400V between these! Be aware!! :-)
While writing this and looking for more information i stumble over this video
With links to schematics for the power supply. According to these it might have been R3 (470k) that were open circuit in my HP8920B.
/Magnus, SM7UGO
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I had a similar issue with my 8920B. In my case it was a resistor that went open circuit, without any sign of burns or high temperature. Unfortunately I cant remember where i found the information about this so I just write what I remember.
The resistor should have a value like 1 Mohm and serve as some kind of kickstart for the switching circuits. It also serves as a bleeder for the main "bucket" capacitor, so this will remain charged at a high voltage level for a long time! Be aware! And two of the heat sinks are connected to each side of the capacitor so you might have up to 400V between these! Be aware!! :-)
While writing this and looking for more information i stumble over this video
With links to schematics for the power supply. According to these it might have been R3 (470k) that were open circuit in my HP8920B.
/Magnus, SM7UGO
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The little green LED is for the supply that keeps the OCXO warmed up and ready for use. The instrument won't come on if that supply goes. Check to see if it is on. If it isn't, you will have to remove the power supply. Not a simple job. Once you have it out, the board for that supply is where the green LED is. Mine went out and I had to replace 2 electrolytic capacitors. I couldn't easily locate two of the exact value, but getting close was good enough.
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Most likely it is the capacitors in the power supply.? I am not sure about the 8920 but the 8924 which is similar has a green led that is seen from the back near the AC power input that stays on when it is plugged in.? Look in the files section for the power supply issue.
Ralph ku4pt
On Thursday, January 12, 2023 at 10:35:05 PM EST, ka2qep@... <ka2qep@...> wrote:
The 8920b won't turn on. No smell, no back fuses. Nothing warm seen with my FLIR IR VIEWER. Was working the evening before. Any ideas? This is typical.? I measured 1.4Megohms across the AC SUPPLY input. Thank you, Bill
_._,_._,_
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The 8920b won't turn on. No smell, no back fuses. Nothing warm seen with my FLIR IR VIEWER. Was working the evening before. Any ideas? This is typical.? I measured 1.4Megohms across the AC SUPPLY input. Thank you,
Bill
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Re: Sync Separator diagram.
Google translate does a really nice job translating this webpage to English.? Not necessary to have an expert in the family.? ?:)
On Tuesday, December 27, 2022 at 09:22:13 AM EST, w9dkc <w9dkc@...> wrote:
Lucky for me - my wife speaks Portuguese.? She's from Rio.
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Re: Sync Separator diagram.
Lucky for me - my wife speaks Portuguese.? She's from Rio.
So, the one with the LM1881 IC needs no adjustment. I'll try that one, maybe both as a comparison. I already have the LM393. I'll post my results.
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Re: Sync Separator diagram.
?
This is the one I used.
?
Use the circuit from fig 1 of the LM1881 data sheet??connect the?LM1881 video input (0.1uF to pin 2)?in parallel with the 8200 video input. Composite sync (pin 1)?to the 8200 H sync input, Vertical sync (pin 3) to the 8200 V sync input.
?
Ralph ku4pt
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Re: Sync Separator diagram.
I think this could help you.
Miguel
73 de PY3MM
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Re: Sync Separator diagram.
?
To use the GBS-8200 converter with the hp-8924c service monitor.
?
Obtain:
?
LM1881N IC sync separator
.1 UF capacitor--2 required
680 K? ohm resistor
?
To be mounted on the GBS8200 board will be 4 SMD 50 K ohm resistors.??
Without the resistors the display will seem to work for?
about 30 seconds and fade out. That is what it did for me.
?
On the LM1881 connect pin 1 to the # 4 (gray wire) pin of the 8 pin RGBS input connector.
Pin 2 to a .1 UF capacitor and then to? the Green input of the 8 pin RGBS connector?
A wire from that junction goes to the input from the 8924C.
Pin 4 to ground.
Pin 6 has a .1 UF and 680 K resistor in parallel to ground.
Pin 8 goes to 5 volts.
Pins 3,5,7 are not used.
?
The 4 SMD 50 K ohm resistors are soldered across capacitors 29,32,33, and 36 on the?
GBS8200 board.? They are in a row between the 3 pots and an IC.
?
This will provide a green video output to a VGA monitor.
?
Ralph ku4pt
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Re: Sync Separator diagram.
Look at the lm1881 datasheet. A lm1881, a capacitor and a resistor and you are set.
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Re: Sync Separator diagram.
if you just search this message board you will find it??
There are a couple of different versions? ...the one based on the LM1881 seems to be the easiest the one suing the LM393 may be the cheapest?
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Re: Sync Separator diagram.
Hi,
Have a look on the British Amateur Television Club website batc.org.uk where you might find something suitable in a back-issue of the CQ-TV magazine, or alternatively search on the forum.
Happy hunting,
Frank,
G0CFD.
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Several years ago I sent the CGA to VGA converter and other parts to a guy who said he would build it for me. I never heard from him again. Now, I have some good reasons to get the screen on a big monitor. I bought the GBS-8200, a perf board and the IC but no longer have the schematic to get it to sync. Looks like I will be doing this one myself. Anyone have it?
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Re: HP8920B Controller Battery
Hi Robert
SAFT makes 3.0V lithium cells, can be had with wire ends to overcome any mounting problems.
George G6HIG Dover UK
On Monday, 19 December 2022, 01:07:49 GMT, Robert G8RPI via groups.io <robert8rpi@...> wrote:
I agree with BIll M with one exception.
The "battery" is a Lithium Primary Cell. It is a slightly odd chemistry, Panasonic BR2/3A 3.0V. They can be hard to find. More common 3.6V cells will work fine but there is a nasty "gotcha". The package has two pins on one end and one on the other but the polarity differs between chemistries / voltages! DOUBLE CHECK POLARITY before fitting a replacement cell. If incorrect you can snip one pin off and fit the cell at an angle. The BR2/3A has 2 pins on positive.
Robert G8RPI.
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Re: HP8920B Controller Battery
I agree with BIll M with one exception.
The "battery" is a Lithium Primary Cell. It is a slightly odd chemistry, Panasonic BR2/3A 3.0V. They can be hard to find. More common 3.6V cells will work fine but there is a nasty "gotcha". The package has two pins on one end and one on the other but the polarity differs between chemistries / voltages! DOUBLE CHECK POLARITY before fitting a replacement cell. If incorrect you can snip one pin off and fit the cell at an angle. The BR2/3A has 2 pins on positive.
Robert G8RPI.
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Re: HP8920B Controller Battery
Hi
The battery is the same on the 8921A and the 8920A. As you
mention it is on the board that the I/O Card Slot is on.
The battery on my models retain the settings for all the options
and sub-routines for running the unit, including the time and the
self test.
At switch on the system does a self check (POST) and also runs a
Test program that checks the functions of all the features and
options that are fitted. So these tests are using all the circuits
of the instrument. They reside in the MCU Prom, with other
optional functions also within that board.
Once the system tests are successful, the screen announces that
all is OK and the boot up RX screen is displayed. Certainly the
battery is the backup for the system time / date, which is set via
the maintenance program. This is probably why, without the
battery, it will not boot up and a message is displayed
? " memory unable to be accessed".
The battery is a Silver Mercury type, which will run for up to 10
years. HP recommend it be replaced every 4 years.
The manual available on this forum can be used to mechanically
access the Battery , removal of covers etc. Be careful to clear
the adjacent board when extracting the memory board, it can foul
on a heatsink on the MCU Board.
These instruments are the top units from and era when we were all
fired up to get to the Moon. Every detail is checked and
considered in the design.
Have Fun
Bill M. VK6IC
?
On 13/12/2022 5:40 am, Ralph Mowery via
groups.io wrote:
toggle quoted message
Show quoted text
The battery backs up anything
in the memory that you program in.? It does not backup
anything critical. It would be similar to when the unit was
first sold with an exception of the clock where you set the
time and date. I am not sure where it is in the 8920, but it
is on the circuit board where the external memory card plugs
in on the 8924.? There should be some pictures of the 8924
battery replacement in the files section.?
I guess it could be like any
other battery and could leak.
I do not know if the voltage
is checked in the self check.
Ralph ku4pt
On Monday, December 12, 2022 at 03:01:02 PM EST,
RFI-EMI-GUY <rhyolite@...> wrote:
I have a fully functional
HP8920B and some time ago I bought a replacement lithium
battery for the controller board which I have not
installed.
Questions:
1). What exactly does this battery back up should it fail
or should I change the battery and fail to maintain
voltage? Anything critical?
2) Does the old battery ever leak?
3) Is the battery voltage tested in any of the self check
routines?
|
Re: HP8920B Controller Battery
The battery backs up anything in the memory that you program in.? It does not backup anything critical. It would be similar to when the unit was first sold with an exception of the clock where you set the time and date. I am not sure where it is in the 8920, but it is on the circuit board where the external memory card plugs in on the 8924.? There should be some pictures of the 8924 battery replacement in the files section.?
I guess it could be like any other battery and could leak.
I do not know if the voltage is checked in the self check.
Ralph ku4pt
On Monday, December 12, 2022 at 03:01:02 PM EST, RFI-EMI-GUY <rhyolite@...> wrote:
I have a fully functional HP8920B and some time ago I bought a replacement lithium battery for the controller board which I have not installed.
Questions:
1). What exactly does this battery back up should it fail or should I change the battery and fail to maintain voltage? Anything critical?
2) Does the old battery ever leak?
3) Is the battery voltage tested in any of the self check routines?
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w9dkc
Miguel PY3MM KD5MM
Alexandre Souza