front panel locked up on Gossen SSP Konstanter power supply

[PA0PBZ]

My suggestion to put back the analog part was because of the random Err 5 occurrence but it looks like you already discovered that it had to do with the voltage, so ignore that suggestion for now. Why it was not locked once still remains a mystery though... The 8279 has a dedicated IRQ line to the processor but it looks like the key detection is timer based. I will patch out the 'ignore keyboard' and the turning on of the lock LED and attach it to this post, stay tuned.


Edit: Try attached but don't expect wonders immediately 

[Swake]

Locked Local LED is off now
Unfortunately no other changes, keys are not responsive.
Bypassing POST still works.

The impossible will be done by tomorrow, miracles take a little longer. 4 more empty EPROMs available.

[PA0PBZ]

The impossible will be done by tomorrow, miracles take a little longer. 4 more empty EPROMs available.

Start erasing the obsolete ones!

Strange that the keys still don't work, I'm quite sure I found what they are doing. More code-staring needed I guess...

[PA0PBZ]

I found another interesting point where the KB processing is skipped. not sure why it would do that but try this version.
Still looking to enable the RS232 but there's just too many stuff going on to make an educated guess - yet.

[Swake]

Keys are still locked with patch2 but something changed:

Using the original firmware when only the digital part of the main board is powered both displays show an '-OL' message.
With this patch2 release the displays both show a 0.00 pattern. And my believe is these are the Uset and Iset values or maybe the Ulim and Ilim values.

This is remarkable because when all boards are powered the 4-digit displays show the output voltage Uout (-0.01) and output current Iout (0.00). Pictures from another power supply where the output is switched off also show that same -0.01V. This is why I think what is shown now with patch2 are not the Uout and I out values.

[Swake]

Filmed the LED's sequence at startup in slow motion:

- Power on

- Seemingly random number of LED's come on for about 1/4 of a second, usually different LEDs on every power on.

- Within a fraction of a second:
   - 4-digit displays show all segments and dots
   - Then all LED's come on too.

- Everything stays lit for about 3 seconds. I believe CPU is running the POST now as this can be skipped.

- Then within a fraction of a second between them:
   - 4-digit displays off
   - All LED's off
   - LED's Iout + Pout + LOCAL LOCKED are on again
   - Then displays show '-OL' + LED Pout is off + LED OVP and OTP are on (This is due to unpowered analog board, Iout and LOCAL LOCKED LEDs stay on)

[PA0PBZ]

Right, this is getting real annoying. A lot of decisions in the reset procedure are made based on reading I/O ports where I have no idea what devices may be connected to that ports. Even with the full schematics and datasheets it would still be a lot of work, and without these it is a lot of guessing. It's also possible that by trial and error patching sooner or later we will override safety features and/or set things to fire...
Then there is still the mystery of why is it locked while the RAM was cleared? Is something wrong and is it a safety feature? We certainly don't want to work around that. Is it custom firmware? I don't think so, the keyboard processing is there in the firmware, but if they made a quick patch good luck finding it amongst 100 memory locations that are all involved in the decision to lock or not.

So a few suggestion:

 - Replace the RAM. Since the ROM checksum is disabled I'm not sure the RAM check is even working, who knows it's faulty after all.
 - Try to find an interface, as far as I could see they are obsolete but there must be something out there.
 - Try to find other firmware, based on the model numbers in the ROM there's a few choices. Maybe the ROM is faulty, no way to tell since the checksum is not working.

62N040RU025P
62N040RU050P
64N040RU100P
64N040RU150P
62N080RU012P
62N080RU025P
64N080RU050P
64N080RU075P
Siemens stabizet D2425

Maybe this guy is willing to read the EPROM, he has like 5 boards on offer: https://www.ebay.de/itm/274598338156

I will stop chasing ghosts for the moment, revert to the original firmware and see if I can get the RS232 working, maybe the lock can be cancelled that way.

[Swake]

Yes I understand and support your concern about that patching vs safety.

The RAM was confirmed good in a tester. Without RAM it hangs on the POST at boot. I reconfirmed that today.

No option boards found so far not even seen one installed in the real world yet.

Will try finding a copy of the firmware. Have to say I have not much hope on this one as I do not believe in corruption or custom version anymore. 2 reasons:

• If it is locked because of remote control than also the REMOTE LED should be on.
• It started ones unlocked, meaning we have everything to make it work again.

I have tried many many times to reproduce the unlocked event.

I'll now focus on this because I want it out of our way:
- Finish replacing the electrolytic caps on the main board. Not on the power board, because these are a bit too expensive in this stage of uncertainty and I don't have those values at hand.
- Carefully reflow the main board from the underside with a hot air gun.

[PA0PBZ]

Some thoughts:

Yes, the RAM was tested in a tester, but does it use the same speed? Does it write the same data to the memory locations? Hanging on the POST without the memory doesn't say that the memory is ok.

Copy of the firmware - did you see the eBay link?

I know it once started unlocked, but for me that is an indication that something is wrong, why would it do that? Assuming that there is no voodoo involved it must be some component that's on the edge of reliability and the first candidate for me is the RAM, then the EPROM. Of course you are free to disagree 

[Swake]

Difficult to continue on this one for the moment as I'm in the middle of a somewhat unplanned move to a different room. But this made me review/think/question what was done so far and now I have some questions and this is one about the power supply for the digital part of the board:

What should the trace for Vcc (+5V) look like on the scope in a digital circuit similar to this one knowing it is running at 11MHz and consumes about 350mA. How much ripple is considered acceptable/normal? Are there spikes visible and what would/should these spikes look like or have as maximum level/frequency?