Author Topic: Fixed: HP 54600A from a skip - repair (Read 5176 times)

Maruku · « **on:** March 20, 2019, 11:20:53 pm »

Evening,

Recently I have bought a HP54600A from ebay that seems to have been recovered from a skip

Sent a silly offer cause I was bored and it got accepted

so it seems now I have to fix it.

It had the usual squished screen problem which should be a matter of just replacing two caps, did some dusting whilst I had it apart and checked for any other obvious problems. Poor little bugger is all mangled on the outside plus there are some other "mechanical" issues I'll have to sort.

Anyways, I have replaced the caps and I did get a full screen but not really the result I was expecting to see (pics attached). I have downloaded the schematics so I will do more investigation tomorrow but I was wondering if any of you have come across this kind of a screen?

Cheers

bd139 · « **Reply #1 on:** March 20, 2019, 11:31:14 pm »

I've repaired a couple of these. Not seen that screen before! Check voltages on the CRT module first. If the pots are bent the front panel is probably cracked. It's really cheap nasty PCB.

The last one I did had a cracked motherboard so YMMV with this one. At worst it's got lots of nice parts in it like AD584 and LT1097.

Repair notes I did on the one I scrapped in the end: https://www.eevblog.com/forum/testgear/hp-54602b-oscilloscope-problems-repair/

I may have a power switch bar lying around which will fit as well. I'll dig around in the cupboard when I get a chance this week.

xavier60 · « **Reply #2 on:** March 21, 2019, 02:46:07 am »

Capacitors on the main logic board were regularly burning up on my 54600A.
I have upgraded to the 54645A, three of them. They have had mainly power supply resistor failures so far.

bitseeker · « **Reply #3 on:** March 21, 2019, 03:57:55 am »

Poor little scope. I have one with the squashed display, too, but never saw this kind of scan problem. Hopefully, it's not catastrophic.

Following along...

Maruku · « **Reply #4 on:** March 21, 2019, 08:29:35 am »

Thanks for the input and help.

I will do more measurements today after work.

The PCB behind the keyboard is all broken to pieces, the Erase key broke off somehow

didn't find it inside the scope. But yeah it is a shitty weak PCB. The pots seem to be okay but the shaft is bent. Will do some bodging today

I hope it's only the CRT that's causing problems, before I replaced the caps the scope was working and some buttons too.
Power switch bar is broken but I did find the broken bit in the pouch so I can glue that one.

Mainboard and PSU look okay visually, didn't see any obvious problems.

The crt cathode pcb had some oxidised resistors but when I measured them they had good resistance so I didn't want to start replacing them yet until the caps would prove to fix the squished screen issue.

More pictures to follow.

Cheers

xavier60 · « **Reply #5 on:** March 21, 2019, 09:08:15 am »

It looks a bit like the horizontal frequency is off. I took a rough reading on a 54645A of 19.75Khz

bd139 · « **Reply #6 on:** March 21, 2019, 09:12:00 am »

Quote from: Maruku on March 21, 2019, 08:29:35 am

I hope it's only the CRT that's causing problems, before I replaced the caps the scope was working and some buttons too.

I think there are sync pots on the CRT board. May be worth turning them a bit and see if it picks up sync. It may have been adjusted before out of spec to compensate for the knacered caps and now is in spec so lost sync. I've had that on some old televisions before back when I used to play around with them.

Maruku · « **Reply #7 on:** March 21, 2019, 09:29:45 am »

Cheers, will check the freq and do some adjustments.

In the meanwhile I stitched up the patient. Don't know what I'll do with the missing part of the PCB, thought I could use the "spare un-used buttons" on the board and use a dremel to do a transplant.

bd139 · « **Reply #8 on:** March 21, 2019, 11:26:20 am »

Oh wow that was properly broken! I had one crack across mine on the impact corner where someone had dropped it. That caused enough problems to blow the crap out of some of the switching diodes.

lordvader88 · « **Reply #9 on:** March 21, 2019, 04:48:07 pm »

A skip is like from the garbage or trash pile or dump, etc, but in the UK

Maruku · « **Reply #10 on:** March 21, 2019, 07:09:42 pm »

Yeah like you said, its like from a dump

Anyway, spoke to my colleague who repaired TV's and he said it is very strange and I should try to put the bad cap back in there...
...strange thing is that I did that and now I can see RUN on the screen plus some other stuff but still squished.

The schematic on Keysight isn't much helpfull because my crt unit has a uPC1379C and that is completely different from the uPC1031 found on the schematic I have.
Measured the voltages and they seem fine. I am missing the schematic so I can't measure the H and V sync because I don't know where to probe them.

Reverse engineering time, but I am happy that the HP hasn't died on me yet and seems to work.

bitseeker · « **Reply #11 on:** March 21, 2019, 07:42:21 pm »

Do you have a measurement of the ESR of the original cap? Maybe the replacement is too low and throwing off the timing. It's tempting to install modern super-low ESR electrolytics, but that doesn't always work best.

Maruku · « **Reply #12 on:** March 21, 2019, 07:48:12 pm »

Okay this is stupid but it seems the chassis was bent somewhat and when I loosened up the CRT chassis from the main chassis it did the trick

Looks like there is some strain to the pcb

and that caused the screen problem in the first place, becuase when I bolted it back up I got the same messed up screen.

Did some panel beating to it t

Probably I should check the solder joints now.

bd139 · « **Reply #13 on:** March 21, 2019, 07:51:33 pm »

I reckon it's like mine was. Main board is cracked. Mine was a 54602 and two channels didn't work due to the big castings over the attenuators cracking the board so I gave up and scrapped it. I made a fair bit of cash just for the parts, more than twice what I paid for it and nicked all the good ICs off the main board

Maruku · « **Reply #14 on:** March 21, 2019, 11:19:22 pm »

Didn't find anything obvious so best not to poke into the mainboard too much.

Besides the Erase button which vanished all other buttons work, swapped out the bent trigger encoder with the holdoff for now until I find a replacement or fix it somehow. Heat gun?

Quite chuffed with how the repair ended up, seems the bugger still has some life left in it. Going to take it to work and test how well it measures.

bitseeker · « **Reply #15 on:** March 22, 2019, 05:01:52 am »

Wow, great to see it working again! Good old flexing board problems...figures.

Maruku · « **Reply #16 on:** March 22, 2019, 01:13:17 pm »

I think it's going to be used quite a lot in my lab since I found it has tetris on it

bd139 · « **Reply #17 on:** March 22, 2019, 02:19:53 pm »

Tetris is why the buttons under the screen never seem to work on them

bitseeker · « **Reply #18 on:** March 22, 2019, 08:31:17 pm »

Oh, man

coromonadalix · « **Reply #19 on:** March 22, 2019, 08:40:21 pm »

+1 oh man loll

bitseeker · « **Reply #20 on:** March 22, 2019, 09:09:30 pm »

Quote from: Maruku on March 22, 2019, 01:13:17 pm

I think it's going to be used quite a lot in my lab since I found it has tetris on it

Maybe wire in an old game controller to save the scope's keyboard (and PCB). It'll be the only 54600A customized for gaming (until I pimp mine the same way).

techman-001 · « **Reply #21 on:** March 23, 2019, 09:50:43 am »

Quote from: Maruku on March 21, 2019, 11:19:22 pm

Didn't find anything obvious so best not to poke into the mainboard too much.
Besides the Erase button which vanished all other buttons work, swapped out the bent trigger encoder with the holdoff for now until I find a replacement or fix it somehow. Heat gun?

Quite chuffed with how the repair ended up, seems the bugger still has some life left in it. Going to take it to work and test how well it measures.

Great repair job because it's still a very useful instrument!
I still use my HP 54600A (which I bought brand new in 1994) for development, especially for waveform screenshots for my tech project articles like this one:
http://hightechdoc.net/mecrisp-stellaris/_build/html/project.3temp.sensors.html#lmt01

bitseeker · « **Reply #22 on:** March 23, 2019, 05:54:06 pm »

That's neat. Do you dump the screen via GPIB?

The add-on modules I've seen are rather overpriced, but the FFT + GPIB one (forgot the model number) would be nice to add (though it apparently has a Dallas memory inside that's probably out of power now and unobtainable).

JFJ · « **Reply #23 on:** March 23, 2019, 10:14:43 pm »

Quote from: Maruku on March 21, 2019, 07:48:12 pm

Looks like there is some strain to the pcb and that caused the screen problem in the first place, becuase when I bolted it back up I got the same messed up screen.

A few years ago, I encountered a HP546xxx series oscilloscope with a garbled screen. It may have been the same model as your scope.

To quickly determine the source of fault (main board or display unit), I intended swapping the display chassis with one from another, working, 546xxx. That, however, became unnecessary when I noticed green flakes on the end of the first chassis screw removed. The end of screw had gouged through the main board's solder mask and shorted an underlying PCB trace to chassis ground.

So, it was a simple repair - touch-up the solder mask and fit shorter screws.

Forgot to mention, the screws that I removed appeared to be HP originals.

Martin.M · « **Reply #24 on:** March 24, 2019, 08:24:29 am »

Quote from: bitseeker on March 23, 2019, 05:54:06 pm

The add-on modules I've seen are rather overpriced, but the FFT + GPIB one (forgot the model number)

that`s much interesting,
I have a 54650 HPIB at back of my 54601A, but FFT would be very nice for playing with the oldie


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Author Topic: Fixed: HP 54600A from a skip - repair (Read 5176 times)

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