HP 3561A Dynamic Signal Analyzer repair

[slbender]

Well, so far Q200 and Q201 on the analog video board, did turn out to be a TO-66 single diffused 4 Amp / 60 Volt complementary pair.  They were fairly well matched in terms of hfe, at 99 for the NPN and 67 for the PNP part, at low currents.  Both of these older parts seemed to be working and measured OK when off the board.  I'll add some MX-4 compound on them when they get resoldered.  Maybe I should check the smaller transistors too, as something is making the video garbled.  The power resistors seem fine, no burn or overheat spots on the board.  I pulled a few of the 10uF. 'Lytic caps but they too seemed healthy, and above their rated values.

While the scan of the Service Manual had put the polarities of Q200 and Q201 in doubt, since I could not see clearly which way the arrows were pointing, at this point, they do not seem to be the problem.  The "better than" 8 Amp / 150 volt pair of TO-220 parts, while they would have fit nicely, even onto the original heatsinks, the replacements, it seems were not needed.  So its back to square one - again.

Any suggestions?

-Steven

[Cubdriver]

Unfortunately I don't currently have access to the analyzer or manual, but will try to offer further suggestions in a few days.

In the meantime, perhaps take a look at any caps on the power supply rails on that particular board?  I don't know if there are any dipped tantalums on there, but they are infamous for failing shorted (and sometimes imitating matches when they do; yours if present obviously haven't or you'd know it by now). 

-Pat

[slbender]

I've hit so many brick walls with this unit you'd think I'd give up....  Nope, gluten for punishment, I bought a second HP-3561a which has different problems, and it is also a later unit.  DUT #2 is about several thousands newer according to the serial number, and features the CMOS memory board (A42) Option 1 instead of the Bubble Memory board (A65) Option 1.

The video comes up nicely, but it comes up with a 1.2.02 error, and at the default screen you don't see the random noise spectrum, so it has either a noise source failure or an FFT failure of some sort.

Switching the 'known working' Analog Display board into the first set - again, no change, still garbled video.  SO, that rules out that board as the source of the video problem.  Once I get some sleep, I'll try switching some of the set #1 boards into DUT #2 to see where and when that random noise on the default screen returns - if it does.

I'll also try to post pictures of the A42 Circuit Board.

-Steven

[slbender]

Sunday morning- lacking in luck!  I switched in three boards into unit #2 and I got even more errors.... :-

Now with the 03561-66510 Front end, 03651-66515 (Analog to Digital??) board and 03561-66520 FFT boards switched - it seems functionality is even worse...  Now DMA error detected, Front End error, 1.1.00 and now the Start, Auto, Half and Over LEDs are flashing continuously.

OK so that did not help, I will again sleep on this, I suspect mismatched levels, but still no noise displayed on the default screen, guess I was hoping for too much, the boards probably are individually matched to each other, still I thought I'd try and give it a shot...

-Steven

[Floopy]

Reviving an old thread...

I acquired an HP 3561A. Upon power up (after checking caps) I was greeted with a screen shrunk on the vertical axis. After about 20 seconds or so the device shutoff and the "Primary over current" LED turned on. After some time I isolated the problem inside the (S] (T] (U] parts of the power supply (all located in A71). A quick check on the diodes I don't see any of them that are shorted. Although CR100 is not living up to it's expectations. It's a VSK231 and the datasheet says that it should be positive on the case and the two leads should be the cathodes.

Where can I get a replacement for it?
Also my main processor board is different. Most of the parts have a date stamp of 1987.

[Floopy]

More measurments

[Floopy]

FYI:
service manual website, it has both.
http://www.ko4bb.com/getsimple/index.php?id=manuals
Type 3561 in the search bar.

[gabor.dani]

Looks like every one of us have a blown CR100.

I just got my unit for 200$, it is in perfect -I mean absolutely 100% pristine- condition. Not even a scratch. I don't know where it was stored, who used it, but people really did not touch this unit in years.
It did not power on. CR100 was shorted. I replaced it with a 60A dual schottky diode, not it works. Best deal ever.

[unknownsoldier90]

Digging out an old thread again…

I have the same DSA, but mine powers up without errors, but the display isn’t working properly:
https://www.eevblog.com/forum/repair/hp-3561a-dsa-repair-crt-double-deviation-in-x-axis/

Btw: R203 is cracked, but has the correct value of 22 ohms 😬