Sinclair ZX80 / ZX81 / Z88 Forums

Spinnetti wrote: ↑Wed Mar 10, 2021 4:57 pm Thanks for the inputs... I probably shouldn't have dove into the TS1000 in this thread; I appreciate the inputs on that.

A friendly moderator can sort that out if you want!

Spinnetti wrote: ↑Wed Mar 10, 2021 4:57 pm"McKlaud", where would I pick up the white, black and sync levels? Is that off the ULA pins?

I’m not him, but for a TS1000/ZX81 you need an oscilloscope connected to IC1 (ULA) pin 16 (the video/tape output pin).

I asked which ULA you have in your TS1000 in case one of the two older ULA chips is fitted. Although we believe most TS1000 computers would have been manufactured with the last ULA version, it’s possible that not all were, or the ULA has been replaced or swapped since.

Mark

These values are off the TS1500 SCLD pin 53 as this thread is about TS1500.

Hello Sinclair folks!!!

I am the said friend Don that both delivered the TS1000 and took the TS1500 back to try to restore it back to glory.

As for the TS1000, it has the 2C210E with all of it's back porch glory. I found that an Atari 2600 composite mod device is a simple solution. On the TS1000, I can use the FR3, UK2, and UK1 pins for ground, video and 5V. I put a separate RCA port on the back for composite out, allowing both RF and composite signals. My guess is I need to modify the resistance on the Atari mod. As I am in full fledged Sinclair restoration mode, I'll need to get back to check that soon.

For the 1500, I removed the 4116 Drams today. After removal, there was a slight increase to 11v on the 12v rail, but still no -5v. I'm guessing it's time to pull L4. We also still have the original 7805. And even though the voltages look right, I'm thinking I should replace it as well.

Really hoping the ULA isn't toast. Not as easy to replace it as it is on the TS1000.

computergui wrote: ↑Wed Mar 10, 2021 11:36 pm Hello Sinclair folks!!!

Hello

computergui wrote: ↑Wed Mar 10, 2021 11:36 pm As for the TS1000, it has the 2C210E with all of it's back porch glory. I found that an Atari 2600 composite mod device is a simple solution. On the TS1000, I can use the FR3, UK2, and UK1 pins for ground, video and 5V. I put a separate RCA port on the back for composite out, allowing both RF and composite signals. My guess is I need to modify the resistance on the Atari mod. As I am in full fledged Sinclair restoration mode, I'll need to get back to check that soon.

Here is the simple buffer amp that I use

But depending on the TV/monitor, the voltage levels of the video may still not be acceptable. There are other solutions.

computergui wrote: ↑Wed Mar 10, 2021 11:36 pmFor the 1500, I removed the 4116 Drams today. After removal, there was a slight increase to 11v on the 12v rail, but still no -5v. I'm guessing it's time to pull L4. We also still have the original 7805. And even though the voltages look right, I'm thinking I should replace it as well.

Really hoping the ULA isn't toast. Not as easy to replace it as it is on the TS1000.

If the +5V is in spec (between 4.75V and 5.25V) then the 7805 is fine. The SCLD (ULA) should not affect the -5V as it does not use it. The problem looks like it is in the DC-DC converter part of the power circuit, either a faulty diode, faulty capacitor or maybe the inductor. If you can’t get the -5V supply working, then an alternative is to fit DRAM chips that don’t need a -5V supply.

Mark

Thanks Mark. I've read a slew of your posts and threads. Really appreciate all the information you've provided.

I have a bunch of 4164 drams. I assume the removal of pin 1, and wiring 8 to 9 would work if we can't solve the -5v problem?

Still feels like we are in the power circuit and swap out the diodes and/or inductor (?)

Well, I've made some progress. After removing the memory, I discovered the replacement Q2 transistor was shot. I replaced it, and got proper voltage...ish.

I'm now showing 13.5V on the 12V rail and -5.4 on the -5 volt rail.

I'm guessing the D1 12V Zener is shot and will be replacing when it arrives.

Any other things that I should check?

computergui wrote: ↑Thu Mar 11, 2021 12:34 am Thanks Mark. I've read a slew of your posts and threads. Really appreciate all the information you've provided.

I have a bunch of 4164 drams. I assume the removal of pin 1, and wiring 8 to 9 would work if we can't solve the -5v problem?

Yeah kind of. If you remove all the DC-DC converter circuitry (because the +12V and the -5V supplies are no longer needed), the tracks to pin 1 of the DRAM chips will not be connected to anything (apart from each other) anyway. And you can link +5V to the tracks for pin 8 anywhere that is convenient.

Some people have done something similar for the Sinclair ZX Spectrum which also uses 4116 DRAM chips.

Mark

computergui wrote: ↑Sun Mar 14, 2021 3:50 pm Well, I've made some progress. After removing the memory, I discovered the replacement Q2 transistor was shot. I replaced it, and got proper voltage...ish.

I'm now showing 13.5V on the 12V rail and -5.4 on the -5 volt rail.

I'm guessing the D1 12V Zener is shot and will be replacing when it arrives.

Check / test also diodes D5 and D6. Also, I don’t know how good this design is with no load. The 4116 DRAM chips draw typically about 20mA to 30mA each when being accessed.

Try connecting some 1k ohm or 820 ohm resistors across the +12V and 0V/GND to see if the voltage drops nearer to the maximum specification figure of 13.2V

It’s still a good idea to replace the 12V Zener.

One other consideration, if one or more of the 4116 DRAM chips are faulty, they may have been the cause of TR2 overheating and dying.

Mark

1024MAK wrote: ↑Sun Mar 14, 2021 4:18 pm
Check / test also diodes D5 and D6. Also, I don’t know how good this design is with no load. The 4116 DRAM chips draw typically about 20mA to 30mA each when being accessed.

Try connecting some 1k ohm or 820 ohm resistors across the +12V and 0V/GND to see if the voltage drops nearer to the maximum specification figure of 13.2V

It’s still a good idea to replace the 12V Zener.

One other consideration, if one or more of the 4116 DRAM chips are faulty, they may have been the cause of TR2 overheating and dying.

Mark

Thanks Mark! I had already planned that after the diode replacement if I couldn't get the voltages in spec. 16 pin sockets arrive tomorrow, so I'll confirm in the next couple of days.

Appreciate everyone's help!!