Metrix OX8627 non start and OSD disappearing.

Hi, Can anyone assist with schematics for this scope please.
When I bought this 2 years ago secondhand, it was perfect, hardly used and immaculate condition. It worked flawlessly until one evening when I left it powered on the bench while I had a meal, maybe 2 hours total. When I returned, the OSD had disappeared entirely and none of the front panel controls functioned. I switched it off.
After about an hour, I powered it back on and all was well for maybe 30 seconds then there was a click and the same thing happened again.

After some fault finding, I found that I could prevent the same thing happening if I sprayed freezer on the TL7705 reset generator, I replaced the TL but the issue stayed the same.

I stripped out all the boards and replaced all elcos for panasonic FR types mainly, although none showed any signs of age....I thought it best to do the lot, together with a new Lithium cell since the old one was flat.

Now when I power up, the PSU trips immediately (no, it's not a reversed elco.....first thing I checked)

I can get the scope to power up if I provide about an amp of current to the 5V rail from a bench supply piggy backed on.

However, the OSD still disappears shortly after power up.
It seems I have 2 issues now.

I do notice that the PSU Switched mode tx seems to run hot at around 65 deg C, is this normal for these?

Nothing else gets particularly hot and all voltages seem nominally correct....oh. and I replaced the TL431 reference in the psu for good measure.....no difference.

Schematics would really help.....pretty please
Kind regards

https://www.uploadarchief.net/files/download/metrix%20ox%208627.pdf for the schematic psu, in this topic are more links to schematics https://www.circuitsonline.net/forum/view/121153

[Bericht gewijzigd door fred101 op (36%)]

Op woensdag 19 februari 2025 16:10:03 schreef fred101:
https://www.uploadarchief.net/files/download/metrix%20ox%208627.pdf for the schematic psu, in this topic are more links to schematics https://www.circuitsonline.net/forum/view/121153

Thanks but I have that schematic. It's more necessary to get a schematic of the digital section, in particular, the reset generator....
If I can't fix the reset issue then it's not worth fixing the PSU....if you understand
Thanks

If you can't fix the PSU, then it's not worth fixing the reset issue ;-)
If the PSU is not OK, the rest will have problems. Golden rule of repair, first the PSU perfect, then the rest. Voltages and ripple within specs.

I'm not a fan of coldspray but if that fixed it, then look around that IC, broken traces, cracked caps or resistors (if SMD then even maybe thanks to the coldspray)

Things got worst after replacing parts, so first question the parts. Did you buy the replacement parts via Ebay/Amazon or AliExpress?
Next your work, like maybe a bad solder joint, damaged inner trace caused by desoldering etc, damage due to static discharge etc

I'm also not a fan of replacing parts that are not proven dead. To much chance of getting more problems.

Op woensdag 19 februari 2025 17:06:41 schreef fred101:
If you can't fix the PSU, then it's not worth fixing the reset issue ;-)
If the PSU is not OK, the rest will have problems. Golden rule of repair, first the PSU perfect, then the rest. Voltages and ripple within specs.

I'm not a fan of coldspray but if that fixed it, then look around that IC, broken traces, cracked caps or resistors (if SMD then even maybe thanks to the coldspray)

Things got worst after replacing parts, so first question the parts. Did you buy the replacement parts via Ebay/Amazon or AliExpress?
Next your work, like maybe a bad solder joint, damaged inner trace caused by desoldering etc, damage due to static discharge etc

I'm also not a fan of replacing parts that are not proven dead. To much chance of getting more problems.

I understand and largely agree. I am an electronics engineer with 50 years of experience and I'm confident I can address the PSU issue, it's a simple enough design based on a standard device and format. I can even install a secondary supply with no trouble. I am hampered by lack of schematics and availability of parts from CA mainly.
Of course there could be a damaged PCB but I am confident it's not the case. As for the parts, I know better than to be dodgy parts on auction sites, they were bought from Farnell and Mouser.
I'm not so confident in the reset circuit and have already replaced peripheral parts with zero change to the symptoms. I'd love to have a look/see at the supply rails on a second scope but don't have one atm. When it powers, all displays are super clean and stable and all controls work normally as far as I can tell in the short time it's on.
What prompted the change of elcos was the slight noise in traces and an instability in the position of OSD, I thought it was wise.
I am suspicious of the high temperature of the SM TX when working although all voltages are normal, which would not be the case if there were shorted turns etc. There is provision for mounting a small fan in this scope, which I may do in any case (reliable electronics comes from cool electronics)
I'm very experienced on most kit and have been regarded as something of a master at smps repairs. I ran my own repair company for over 20 years and trained with the MOD.

Goodday,

You can also check on eevblog, this is a more world wide forum.
Maybe there is someone who can help you.

Maybe this will help?

Metrix OX 8620 - 8627(1).pdf

Part two in next frame

Part two:

Metrix OX 8620 - 8627(2) (schema's).pdf

Part three in next frame.

Part three:

Metrix OX 8620 - 8627(3) (print).pdf

Regards,
Luc.

Op woensdag 19 februari 2025 19:09:14 schreef Joris:
Goodday,

You can also check on eevblog, this is a more world wide forum.
Maybe there is someone who can help you.

Thank you...

Op woensdag 19 februari 2025 22:48:49 schreef hobby luke:
Maybe this will help?

[bijlage]

Part two in next frame

Thank you, YOU ARE A STAR SIR !!!
Gary

Op woensdag 19 februari 2025 22:49:53 schreef hobby luke:
Part two:

[bijlage]

Part three in next frame.

Hi Luc
Thank you again sir You are a brighter star
Gary

Op woensdag 19 februari 2025 22:50:39 schreef hobby luke:
Part three:

[bijlage]

Regards,
Luc.

Oh wow....Thank you again Luc,
Your are a star, a gentleman and a scholar.
Much obliged to you.
Kind regards
Gary

Op woensdag 19 februari 2025 19:09:14 schreef Joris:
Goodday,

You can also check on eevblog, this is a more world wide forum.
Maybe there is someone who can help you.

Cheers, I'll try if no luck here.
Gary