Re: TDS754D psu. Totally stumpped.
On a tangent, I’ve been reading through the datasheet of the PFC IC. It’s a
pretty interesting device. As it’s a critical current conduction mode
controller, the switching frequency is variable - both within a mains
cycle, but also depending on load. The higher the load, the higher the
average current in the inductor, and the lower the switching frequency.
Also, the higher the input voltage, the higher the dI/dt, so the higher the
switching frequency.
I guess this means that the power dissipation in the snubber is inversely
proportional to the load and proportional to the input voltage. Fascinating!
I seem to remember the PFC bumping on and off in standby, but otherwise
these PSUs would have absurd standby power usage.
?ann fim., 14. des. 2023 kl. 12:04 skrifa?i Sigur?ur ?sgeirsson via
groups.io <siggi@...>:
toggle quoted message
Show quoted text
On Thu, Dec 14, 2023 at 2:12?AM Vince Geisler <vgeisler@...> wrote:
snubbers, look good, the snubber diode is a bit off, 0.5vf vs published
0.8-1.6vf but its still acting like a diode. gone over the circuit 100
times now. still stumped. Given this is my main instrument I may have to
find a working used on on ebay, and just call this one a loss.
The problem is entirely consistent with a bad snubber network, or else a
leaky CR4 like someone else mentioned.
IRFP450 is only specified for 500V(DS), so boosting to 400V is already
operating pretty near their limit, hence that impressive snubber network.
The one component of the snubber network you haven't mentioned is C10. If
C10 goes high resistance or somehow loses significant capacitance, your PFC
mosfets will blow. Also R135/12/11/134 should be expected to get warm -
otherwise there's no reason for paralleling 4 2W resistors.
Knowing the frequency of the switcher, it's possible to ballpark the
dissipation of the snubber network, as C10 charges to a voltage somewhere
in excess of VBUS (and hopefully less than 500V) each cycle, then
discharges through the resistors when the mosfets close. Assuming 50kHz
switching frequency (the datasheet example), you'd
have (680pF*(400V)^2)/2*50kHz ~= 2.7W. If the spike goes all the way to
500V, you have ~4.25W dissipation in the network. This is obviously all
linear in the average switching frequency of the PFC.
There are sneaky ways to measure the inductive spike across Q5/6 without
additional test equipment, like by tacking in a peak detector using a fast
diode and a HV capacitor, then measuring the voltage across that with a
DMM.
In your shoes I'd replace C10, CR6 and CR4, or else beg, borrow or steal
equipment to take a look at the PFC switching waveform in action. If you're
local to me (Montreal, Canada), you're welcome to pop in and we can put the
patient on the slab, see what's up.
|
Re: TDS520 in Brittany: FAIL++Acquisition FAIL++ Attn/Acq interface
First thing, replace all the SMD electrolytic capacitors throughout the unit, on the processor board, acquisition board, and front panel (maybe the firmface board if fitted and caps are there too? I'm not sure on that model)
I would suggest making note of values, then removing them all, then putting the bare processor board and acquisition boards through the dishwasher.
Washing by hand is fine too if no dishwasher is available.
Repair any damage caused by the leaked electrolyte and install new caps.
If you need a replacement VCO board (the little PCB sticking up off the acquisition board) I made a replacement design, and may have a few spare blank PCB's laying around if you need.
The two segments alternately flashing on the 7-seg display on the processor board indicate that the processor has sucesfully booted and is running, so I'd concentrate efforts on the acquisition board, besides any electrolyte corrosion damage as previously mentioned.
That ROM chip you took a photo of is the boot ROM (basically equivalent to the BIOS in a standard PC), and can be ignored as working as the unit boots ok.
Jared
|
|
|
Re: tunnel diode orientation in Type 284
On Thu, Dec 14, 2023 at 09:50 AM, Shaun M wrote: c. Adjust the front panel TD BIAS control (R132) to its approximate midrange
position. Adjust the internal TD Bias adjustment (R133) for a trace similar to
that shown in Fig. 6-26A. Oh man, I think I have a big red pot on the front right of the inside face where the revised Fig. 6-25 shows R133, but had no idea what it was for. Thanks for pointing this out! Adam
|
Re: tunnel diode orientation in Type 284
On Thu, Dec 14, 2023 at 10:47 AM, Albert Otten wrote:
The change from R133 to R132+R133 occurred at B04000.
Albert
Thanks Albert. Looks like Tek replaced 30k external pot with a 30k internal (R133) + 3k external (R132) pot. TD current would change over a wider range from part to part but once the unit is calibrated to specific diode it makes sense to make only small adjustments. Ozan
|
Re: tunnel diode orientation in Type 284
Yes, I am looking at 070-0754-00, pulse generator (schematic sheet 2). But it must be a later version. It is available on the BAMA site. There is a relevant modification as well (apologies for the formatting):
Section 2 Operating Instructions
Page 2-7 First Column
ADD: the following note after the first paragraph under the heading Pulse
Output:
NOTE An internal TD Bias adjustment (R133) is provided
for coarse adjustment of tunnel diode bias. If the tunnel diode is replaced or if the front panel control doesn’t provide a satisfactory setting adjust the TD bias (internal) in the manner given in the Calibration section of this manual.
Section 4 Maintenance
Page 4-8 Fig. 4-7
REPLACE: the present photo with the one included in this insert, note the
new location of D165.
Section 6 Calibration
Page 6-20 Fig. 6-25
REPLACE: the present photo with the one included in this insert, note the addition of the location of the Internal TD Bias adjustment (R133).
CHANGE: the heading of Step 15 to read: 15. Adjust TD Bias (internal)
REPLACE: the first sentence of Step 15(c) with the following:
c. Adjust the front panel TD BIAS control (R132) to its approximate midrange position. Adjust the internal TD Bias adjustment (R133) for a trace similar to that shown in Fig. 6-26A.
Shaun M
|
Re: tunnel diode orientation in Type 284
The change from R133 to R132+R133 occurred at B04000.
Albert
|
Re: tunnel diode orientation in Type 284
On Thu, Dec 14, 2023 at 09:24 AM, Ozan wrote:
Have you adjusted the coarse bias R133?
There is no R133 in 070-0754-00. Is there a revised schematic?
Ozan
Well, that's a great question. I've seen reference to "coarse bias" but assumed they meant R123, bias balance. My 284 seems to match 070-0754-00 schematics (i.e., there is no R133). The 070-0754-01 manual on TekWiki mentions R133 on page 2-7, but it doesn't include schematics :(. thanks, Adam
|
Re: tunnel diode orientation in Type 284
Have you adjusted the coarse bias R133?
There is no R133 in 070-0754-00. Is there a revised schematic? Ozan
|
Re: TDS520 in Brittany: FAIL++Acquisition FAIL++ Attn/Acq interface
I repaired a TDS520 with exactly same error screen after repairing a (literally) burned power supply. In my case leaking electrolytic caps damaged a trace to U900 on acquisition board.
Ozan
toggle quoted message
Show quoted text
Hi to all usual suspects here.
You will maybe remember you helped me resurect my 7704A from decades of non
working neglect. Thanks!
Here is for me a new challenge. I did a large leap in time from the 7704A and
just bought a TDS520.
At boot:
All ok except:
FAIL++Acquisition
FAIL++ Attn/Acq interface
As soon as I knew it will be coming I read here all I could about it so I know
that Artek has the documents.
Btw I want to praise Artek a bit here. I bought them the service manual for my
two HP8640B I just bought too (yes, two is gluttony, I know but they were
cheap and defective of course, so how to resist?)
Anyway Artek gives a really good service. The manuals are of upmost quality. I
got them instantly and the charge is very reasonable.
I posted the boot to "TDS520 in Brittany"
/g/TekScopes/album?id=291619
Also the 1993 rom: A11U1331 ver 1.5
There's a 7 segments inside at the back which only blinks alternately his two
right segments.
Apart for the fails the scope is in perfect shape and was only very dusty
inside. I disinserted all flat cables I could find and re-inserted them. I
also removed the dust with hope this will change the fail boot (not really!)
It did not.
All advices will be received gratefully.
|
Re: tunnel diode orientation in Type 284
Adam,
For your reference, I checked the voltages at J135/J145 in a working 284:
Measured +- 11.8v (working with pulse output)
Low limit: +-9.9v
High limit +- 14.9v
So the adjustment range using R133 + R132 is about +-9.9v to +-14.9v
Have you adjusted the coarse bias R133?
Shaun M
|
Re: tunnel diode orientation in Type 284
I get about 27.2V differential at bases of Q130 and Q140, and about the same
between positive and negative peaks at J135 and J145. Well short of the ~30V
needed.
With TD BIAS at mid point and assuming a linear pot, swing at Q120/125 should be about 20V*(11.1k // 30k)/(2.2k+11.2k//30k)=15.7V single ended but your scope shot shows ~ 13V. Low point is ~ 0V so the issue seems to be at peaks. If you short TP11 to ground, do you see +17V/-17V at collectors of Q120/125 with max TD BIAS? 1) Is it possible +20V/-20V is sinking to a lower voltage during trigger time? 2) Is base of Q125 at ~ -0.7V 3) is it possible resistors R121 and R129 drifted to higher values? There are not many possibilities around this part of the circuit, next would be to suspect the transistors. TD could still be bad but without this section working even a good TD won't function. Ozan
|
TDS520 in Brittany: FAIL++Acquisition FAIL++ Attn/Acq interface
Hi to all usual suspects here. You will maybe remember you helped me resurect my 7704A from decades of non working neglect. Thanks! Here is for me a new challenge. I did a large leap in time from the 7704A and just bought a TDS520. At boot: All ok except: FAIL++Acquisition FAIL++ Attn/Acq interface As soon as I knew it will be coming I read here all I could about it so I know that Artek has the documents. Btw I want to praise Artek a bit here. I bought them the service manual for my two HP8640B I just bought too (yes, two is gluttony, I know but they were cheap and defective of course, so how to resist?) Anyway Artek gives a really good service. The manuals are of upmost quality. I got them instantly and the charge is very reasonable. I posted the boot to "TDS520 in Brittany" /g/TekScopes/album?id=291619Also the 1993 rom: A11U1331 ver 1.5 There's a 7 segments inside at the back which only blinks alternately his two right segments. Apart for the fails the scope is in perfect shape and was only very dusty inside. I disinserted all flat cables I could find and re-inserted them. I also removed the dust with hope this will change the fail boot (not really!) It did not. All advices will be received gratefully.
|
Re: Need/want a bench top DC power supply.
Hi,
I use a Topward 6306A (Linear design, Separate Voltage and Current Analog Meters, Dual 30V @ 6A, 5V @ 5A), Topward 6603D (Linear design, Separate Voltage and Current Digital Meters, Dual 60V @ 3A, 5V @ 5A) as my main go-to Bench Supplies. I purchased them cheap and fully rebuilt them (including fans), they work well. You might consider something like that.
I also have a Kikusui PAD-L 35-50 (Linear design, 35V @ 50A) and an HP 6032A (Switcher design, 60V @ 50A -1000 V-A) for bigger stuff.
Ross
toggle quoted message
Show quoted text
-----Original Message----- From: [email protected] < [email protected]> On Behalf Of Mark Litwack Sent: Thursday, December 14, 2023 7:58 AM To: [email protected]Subject: Re: [TekScopes] Need/want a bench top DC power supply. Sorry - Just noticed your price target in a later post. The Aim-TTi MX models are going to be quite a bit more than $100-$150. -mark
|
Re: TDS754D psu. Totally stumpped.
On Thu, Dec 14, 2023 at 04:12 PM, Vince Geisler wrote:
Jared,
yes, as far as i can understand, Q5,6 are for for PFC. They step the 120vac
wall power to 400V. That part seems to work fine in standby. I can leave it in
standby forever and its fine.
It goes Caddywhompus as soon as I turn on the scope, at which point it will
blow up immediatly to as long as running for 15 min (the record so far). Using
your board, it will run, except for when the thing randomly goes pop, nothing
heats up. No hot spots at all using the ir thermometer. Its the darndest
thing. Most frustrating is not having a scope to look at some of the signals
from U10,U9. This is my sole unit.
snubbers, look good, the snubber diode is a bit off, 0.5vf vs published
0.8-1.6vf but its still acting like a diode. gone over the circuit 100 times
now. still stumped. Given this is my main instrument I may have to find a
working used on on ebay, and just call this one a loss.
Thanks for the tester board. I would not have gotten this far without it. and
thanks for all the ideas.
I'm glad the tester is proving useful. :) If you end up needing a new PSU to get by, I have a couple tested working variants here if you don't find something more locally. Message me privately and we can work something out if needed. (I am in Japan, but postage shouldn't be toooo bad). Jared
|
Re: TDS754D psu. Totally stumpped.
On Thu, Dec 14, 2023 at 2:12?AM Vince Geisler <vgeisler@...> wrote: snubbers, look good, the snubber diode is a bit off, 0.5vf vs published
0.8-1.6vf but its still acting like a diode. gone over the circuit 100
times now. still stumped. Given this is my main instrument I may have to
find a working used on on ebay, and just call this one a loss.
The problem is entirely consistent with a bad snubber network, or else a leaky CR4 like someone else mentioned. IRFP450 is only specified for 500V(DS), so boosting to 400V is already operating pretty near their limit, hence that impressive snubber network. The one component of the snubber network you haven't mentioned is C10. If C10 goes high resistance or somehow loses significant capacitance, your PFC mosfets will blow. Also R135/12/11/134 should be expected to get warm - otherwise there's no reason for paralleling 4 2W resistors. Knowing the frequency of the switcher, it's possible to ballpark the dissipation of the snubber network, as C10 charges to a voltage somewhere in excess of VBUS (and hopefully less than 500V) each cycle, then discharges through the resistors when the mosfets close. Assuming 50kHz switching frequency (the datasheet example), you'd have (680pF*(400V)^2)/2*50kHz ~= 2.7W. If the spike goes all the way to 500V, you have ~4.25W dissipation in the network. This is obviously all linear in the average switching frequency of the PFC. There are sneaky ways to measure the inductive spike across Q5/6 without additional test equipment, like by tacking in a peak detector using a fast diode and a HV capacitor, then measuring the voltage across that with a DMM. In your shoes I'd replace C10, CR6 and CR4, or else beg, borrow or steal equipment to take a look at the PFC switching waveform in action. If you're local to me (Montreal, Canada), you're welcome to pop in and we can put the patient on the slab, see what's up.
|
Re: Need/want a bench top DC power supply.
On 12/14/2023 1:22 AM, sknaugler@... wrote: On Wed, Dec 13, 2023 at 09:54 PM, Bruce Lane wrote:
??? What would you think of a Lambda/TDK GEN50-30?
??? Specs here:
??? I have a spare. Let me know! At first glance your unit would fit the bill, although a boxy unit that would sit on a bench would be better than a rack mount.
But, at least after seeing what those TDK 50-30 units sell for on eBay, maybe not.
I really should have mentioned that I am a retired engineer and now hobbyist. I was thinking along the lines of sub $50 for a fixer upper to maybe $100-$150 for an older bench top unit.
I guess that I'm a little surprised that that nobody has mentioned this "Red 0-30V 2mA-3A" from ebay as a way to update old boat anchors. This design as supplied has some serious flaws but they are easy to overcome. I have done three of these using ten-tern pots, DPMs, and other mods and they all turned out nicely. -- Bert
|
Re: tunnel diode orientation in Type 284
I've done that when verifying TD functionality while troubleshooting some time-bases. Ozan suggested how to do it and it works very well. Sort of gratifying to watch that jump when the TD fires.
Barry - N4BUQ
toggle quoted message
Show quoted text
----- Original Message ----- From: "Albert Otten" <aodiversen@...> If you want to check the TD that way, it's save in my opinion. Suppose you have
a variable DC power supply 0-15 V.Then with a 560 ohm resistor the supply can
source some more than 21 mA to the TD, but not excessive. First reliably
connect DC minus to 284 GND. Then a lead to DC plus and at the end of the lead
the resistor. Now you can touch the inner connector of the GR output with the
free resistor end. But grep the resistor only at the DC end, not the GR end.
To see what happens you can put an ammeter in series with the lead and a
voltmeter across the GR connector. Crank up the DC voltage slowly until the TD
fires.
|
Re: Need/want a bench top DC power supply.
Sorry - Just noticed your price target in a later post. The Aim-TTi MX models are going to be quite a bit more than $100-$150.
-mark
|
Re: tunnel diode orientation in Type 284
Hi Adam
My 284 isn't cooperative today, refused to produce an output pulse. Two days ago I think it started (after heating up somewhat with a f?hn) but then the scope broke down. (Extreme bright display, likely a grid DC restorer problem.) Anyway, I measured at maximum about 28 or 28.5 V across the air;line. Even with the +20V set at maximum (20.7 V) no firing TD at all.
Perhaps time for me to recheck the TD via the output connector.
If you want to check the TD that way, it's save in my opinion. Suppose you have a variable DC power supply 0-15 V.Then with a 560 ohm resistor the supply can source some more than 21 mA to the TD, but not excessive. First reliably connect DC minus to 284 GND. Then a lead to DC plus and at the end of the lead the resistor. Now you can touch the inner connector of the GR output with the free resistor end. But grep the resistor only at the DC end, not the GR end.
To see what happens you can put an ammeter in series with the lead and a voltmeter across the GR connector. Crank up the DC voltage slowly until the TD fires.
When orientation of the TD seems wrong then repeat things with DC plus and DC minus interchanged. And don't forget to remove the internal supplies from Q135/Q145.
Albert
|
Jared Cabot
Shaun M