TS1000 Diagnostic Help

[DeLorean_4]

I just tried powering it up with the RAM pack installed and there's no difference whatsover.
I guess that only leaves the ROM?

[1024MAK]

It may be the ROM, but it may also be a poor connection on the PCB.

Which chips are in sockets?

From your previous posts, I'm assuming you have both a digital multimeter and an oscilloscope. How many channels does it have? Do you have any other test gear?

Mark

[Moggy]

Sockets can be problematic too. I find the ROM socket to be the worst. I recently fitted three new ROM devices I had made up and all three gave blank screens some judicious pressing of the chip ( NOT RECCOMENDED IT'S JUST THAT I DON'T CARE ABOUT THE CONSEQUENCES) produced a temporary flash of life, replacing the sockets ended the matter.

I also nearly binned a pristine ZX80 until Mark insisted the CPU socket was at fault and I finally bit the bullet and listened to him.
The point being it's not only the active components that cause problems, the passive sockets can be just as bad and the fact that things worked then suddenly didn't after replacing parts would mean it's something worth looking at.

Just because putting a pointy multi meter probe at the top and bottom of the socket produces continuity don't automatically think it's OK as the flat sided chip pins may not have the same friction fit contact especially if they are tarnished (Mostek ROMS especially)

Just something to consider and if you feel it's definitely the ROM and you are fairly local I'm sure I can post you something.

[1024MAK]

Touching a chip pin with a probe may well result in said pin making electrical contact with the socket, or with the solder joint, hence giving misleading test results. Then when the probe is removed, the symptoms will return or change.

The first thing to do with any existing sockets, is to use a good magnifying glass under a very good light, and compare each contact with the adjacent contacts and with any other contacts in the same socket, or with other sockets of the same type. Each contact should grip the leg of the chip.

Single wipe sockets (where there is metal only on one side) are far more likely to cause problems. The other cause of poor socket contacts is where either chips have repeatedly been inserted and removed, or where an expansion has been plugged in and distorted the socket contacts (e.g. an internal UDG board).

Mark

[DeLorean_4]

It may be the ROM, but it may also be a poor connection on the PCB.

Which chips are in sockets?

From your previous posts, I'm assuming you have both a digital multimeter and an oscilloscope. How many channels does it have? Do you have any other test gear?

Mark

All of the chips are on factory-installed single wipe sockets. My oscilloscope has 4 channels. I have no other test gear because my only goal was, and is, to repair my father's TS1000 and 2068 and enjoy them.

I haven't mentionned my misadventure on the TS2068 yet.I got it to work flawlessly for a while, and then it started developing new faults, some of which may point to a bad SCLD chip. I'll open up that can of worms in another thread when I'm done with the 1000.

I think my next step on the 1000 is to deep dive the socket contacts. I'm parallel pathing a new ROM chip as well.

[DeLorean_4]

I got a known good ROM chip from another member here.

The computer worked for a few minutes, and then it went to its old ways.

Whatever issue is afflicting this machine is a very borderline failure that heals itself for a few minutes after 3 weeks of rest.

My top suspect is a bad contact somewhere.

The last thing I haven't changed on this machine is the RAM chip.

[DeLorean_4]

It started working again after I had gone through and improved the contacts at the ROM socket (expanding each leaf of the socket).

I was getting ready to put the computer back in its case, and now it's back to a blank screen. This is driving me crazy.

[DeLorean_4]

All of the factory IC sockets are single-sided leaf-type.
After some generous use of contact cleaner (particularly on the Z80 and vLA81 legs and sockets) I noticed I could get life from the computer again. Initially just a few minutes at a time, and I'm now at around 15 minutes. I have also been able to go directly from a failure state to a working state (TWICE! )by removing the chips, applying contact cleaner, and re-installing both the Z80 and vLA81.

With the equipment I have, I'd be worried about damaging traces when replacing the sockets. My preferred plan of attack would involve cleaning the ones that are currently there.

I have read that di-electric grease would not help. Is this indeed correct?
I do not have an ultrasonic cleaner (at least yet).

Would anyone here be able to recommend a method for cleaning the socket contacts?

[Moggy]

If you don't wish to remove the socket you could at least try re-flowing the solder joints. some of the pins make contact on the top side of the board so perhaps check and see if these look solid.

In my own actual experience with the ROM socket I always ended up either replacing or soldering the chip directly to the board,
( as no amount of cleaning worked), which I understand you don't want to do but should consider it a last gasp option if all else fails and you are convinced it is a socket problem. I have come to consider the cheap and cheerful ones fitted by Sinclair are one shot affairs insofar as once the chip is fitted leave it alone.

As an afterthought, the 15 minute thing leads me to think that heat somewhere on the board is playing a part in all this.

[DeLorean_4]

Thanks Moggy. I agree that that's probably what I'll end up having to do. It's funny how after a while IC sockets end up being a nuisance rather than a blessing.

On the topic of heat, I ran some experiments to rule it out (As a side note: none of the ICs ever got hot). After a 15 minute failure, I would leave the computer alone for a while in my cold basement and come back: plugging it back in wouldn't work. I then re-applied contact cleaner, ran it until it failed, quickly removed the ICs, applied contact cleaner to just the sockets, and re-installed the ICs, and the computer worked right away. I repeated that experiment three times in a row, the computer would reliably fire right back up.

Since writing my last post, I tidied up my workshop area because the TS1000 was just a temporary guest on my disassembled TS2068's turf.
Re-assembling everything resulted in nothing turning on anymore.
I then disassembled the bottom half of the case. Plugged it in, it worked.
I subsequently re-installed the bottom half while the computer was on to see if torquing a certain fastener would trigger the failure.
I didn't encounter any throughout that second re-installation, I didn't torque any of the fasteners more than I had to.

Last night, the computer was reliable enough for me to play around with my printer for around a half hour before I called it quits.

I plugged in the computer this morning and it fired right up.
I returned from work, plugged it in, and it fired right up.
I plugged it in just now before hitting the "Submit" button, and it still fired up.

Even my membrane keyboard works 100% again

I won't touch anything ever again on this computer unless I absolutely have to. I had plans for a composite mod, but I'll leave it alone.