Faulty Z88 - common problems?

[pyoorkate]

Hi folks,

So I took my Z88 with me on vacation - and when I got there, sadly, I found it had become faulty. Initially it wouldn't turn on (using the existing batteries or the AC supply). It emitted a high-pitched whine when I removed and returned the same batteries - or connected it to the AC supply (by high pitched, I mean at the range limits of my hearing). That noise I often associate with HF power supply problems. A soft reset did nothing.

Following a hard reset, it worked fine for about 10-15 minutes before locking up and emitting that same whine.
Following another hard reset it worked again for <30 minutes before locking up - this time the screen went completely black, and again, that same whine.
New batteries, both packs removed (1M Flash, 128k RAM) and another hard reset and the same symptoms persist (working for a short period then either: locking up, completely black screen, or mostly blank screen with some random text in the bottom right corner)

It's going to take me a little bit to get to digging into it (my desk is currently covered in a lot of projects), but before I do are there common faults with these that people have seen? And I haven't seen one linked anywhere, but is there a proper service manual available?

In case it matters, it also has a 512k RAM upgrade and a OZ4.7 hardware upgrade.

Thanks!

[Chris_68]

Hi,

Sorry to hear you're having problems with your Z88.
Just a quick reply, will try to contribute more later.

Service manual https://cambridgez88.jira.com/wiki/spac ... d=31555597
Fault diagnosis https://cambridgez88.jira.com/wiki/spac ... and+Repair

Has it worked ok earlier on with you upgrade?

When you have time, check the voltages before and after it freezes, start with the voltages for RAM/ROM. Then in section 4.2 you have voltages for the transistors.



Regards
Chris

[pyoorkate]

Thank you for the links!

It *appeared* to be working fine. I used it a few times - at least once to do some longform writing, and once for a video (where I had it switched on for a fair period of time). I also had it on for a while when I was getting the serial file transfer set up, and at no point did it exhibit any of these symptoms.

[Jbizzel]

The high pitch whine is a good think. Means the super cap is charging

[okto]

The high pitch whine is a good think. Means the super cap is charging

Not sure this is true. To my understanding, the supercap charges via one of the DC rails, not a charge pump or inverter, so it shouldn't make any sound at all. High-pitched whine usually means a bad switching power supply; IIRC, the Z88 has one in order to provide bipolar 5V rails and the >=12V (don't remember the exact voltage, either 12 or 21V) to burn EPROMS.

I imagine you're thinking of the way a camera flash works, where a relatively low battery voltage runs a charge pump to charge a higher-voltage (350V or more) capacitor. The supercap in the Z88 is low voltage and just drinks plain DC.

[Jbizzel]

All mine make a whine when first turned on after a while being totally flat.

This comes from the Z, itself.

If you remove power for a minute or two, then reconnect the whine doesn't happen.

If I leave if disconnected for 10 minutes, the power it up, the whine starts again.

I have assumed this is the super cap.