TS1500 no video

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Spinnetti
Posts: 253
Joined: Sat Sep 12, 2020 11:29 pm

Re: TS1500 no video

Post by Spinnetti »

Thanks Gents, I appreciate the learning exercise.

So, if I want to try and test the transistor, is that with or without power on? (sorry for the dumb questions lol)
Also, any easy way to test the caps rather than just random replacement? I don't mind replacing, but want to see if the thing is going to work or not first!

Thanks!
Zeddy: ZX80, ZX81/ZXpand, TS1000/ZXpand, TS1500/Zxpand+
Speccy: 48k, +, +2, +3, TS2068, "Bare Metal" Pi, Next KS2, IF1/Microdrives/Vdrive/Light Gun/VGA-Joy
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C5: 24v, LiFE battery, Disc brakes
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1024MAK
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Re: TS1500 no video

Post by 1024MAK »

Spinnetti wrote: Fri Jan 29, 2021 2:27 am Thanks Gents, I appreciate the learning exercise.

So, if I want to try and test the transistor, is that with or without power on? (sorry for the dumb questions lol)
Also, any easy way to test the caps rather than just random replacement? I don't mind replacing, but want to see if the thing is going to work or not first!

Thanks!
Definitely without power on!

Even better if you test it after having removed it from the PCB, as other components in the circuit can affect the results.

Mark
ZX81 Variations
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ZX81 Video Transistor Buffer Amp

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1024MAK
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Re: TS1500 no video

Post by 1024MAK »

For testing the electrolytic capacitors, you need a capacitor tester that can test both the capacitance AND the ESR. Further, to do these tests properly they need removing from the circuit (PCB). So as they don’t cost much, its easier (and better) to just renew them.

With fault finding, you have to take it one step at a time. There may well be other problems. Due to the interaction between the various components, it’s not always possible to say with any certainty that if you do X, then Y will be okay.

So the first stage to to get the power supply systems working. Only once the power supply systems are stable and reliable is there any point in trying to fault find the digital systems (RAM, ROM, Z80) and the ULA.

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
Spinnetti
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Joined: Sat Sep 12, 2020 11:29 pm

Re: TS1500 no video

Post by Spinnetti »

Got it, thanks. Will pull the transistor in the morn and test it and go from there.
Zeddy: ZX80, ZX81/ZXpand, TS1000/ZXpand, TS1500/Zxpand+
Speccy: 48k, +, +2, +3, TS2068, "Bare Metal" Pi, Next KS2, IF1/Microdrives/Vdrive/Light Gun/VGA-Joy
QL: Minerva/QL-VGA/Custom PSU
C5: 24v, LiFE battery, Disc brakes
Spinnetti
Posts: 253
Joined: Sat Sep 12, 2020 11:29 pm

Re: TS1500 no video

Post by Spinnetti »

following the link, transistor seems ok? (open between base and both legs) Anyway, since I'm gonna order stuff, what else might I want to order so I can get at one time? Power transistor, all the caps?....

Thanks!
Zeddy: ZX80, ZX81/ZXpand, TS1000/ZXpand, TS1500/Zxpand+
Speccy: 48k, +, +2, +3, TS2068, "Bare Metal" Pi, Next KS2, IF1/Microdrives/Vdrive/Light Gun/VGA-Joy
QL: Minerva/QL-VGA/Custom PSU
C5: 24v, LiFE battery, Disc brakes
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1024MAK
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Re: TS1500 no video

Post by 1024MAK »

I assume you used the resistance range on your multimeter?

Does your multimeter have a diode test range?

If yes, do the following:
Get a drawing showing which pin is which (e,g, a manufacturer data sheet). For example this one.
  1. Connect the positive (red) meter lead to the base. Connect the negative (black) meter lead to the collector. Note the result.
  2. Connect the red meter lead to the base. Connect the black meter lead to the emitter. Note the result.
  3. Connect the black meter lead to the base. Connect the red meter lead to the emitter. Note the result.
  4. Connect the black meter lead to the base. Connect the red meter lead to the collector. Note the result.
  5. Connect the red meter lead to the collector. Connect the black meter lead to the emitter. Note the result.
  6. Connect the black meter lead to the collector. Connect the red meter lead to the emitter. Note the result.
For Q2 which is a PNP bipolar type, tests 1, 2, 5 and 6 should give the over-range or open circuit indication (the exact indication depends on your multimeter).
Tests 3 and 4 should give a result between about 0.55V and 0.65V

If any test gives a zero or near zero result, the the transistor is dead.

Mark
ZX81 Variations
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ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
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1024MAK
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Re: TS1500 no video

Post by 1024MAK »

This is the relevant circuitry:
Image

Note that I believe that diodes D7, D8 and D9 are shown the wrong way round (incorrect polarity) in this diagram. I can’t check, because I don’t have access to a TS1500. They are hard to find in the U.K...

If transistor Q2 (ZTX750) is okay, then something else is wrong.

As well as the other items that have already been mentioned, it’s worthwhile getting some spare diodes:
  • 1N4002 or 1N4003 through to 1N4007 (the higher numbered parts are just rated at a higher breakdown voltage),
  • 1N4148 (get at least five of these, they are very cheap)
  • BA221 (you may have difficulty getting any of these at a reasonable price, in which case get a BA157 diode instead)
Mark
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TS15000 DC-DC Converter circuitry
TS15000 DC-DC Converter circuitry
ZX81 Variations
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ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
Spinnetti
Posts: 253
Joined: Sat Sep 12, 2020 11:29 pm

Re: TS1500 no video

Post by Spinnetti »

Thanks, I'll order some stuff, and keep going... :)
Zeddy: ZX80, ZX81/ZXpand, TS1000/ZXpand, TS1500/Zxpand+
Speccy: 48k, +, +2, +3, TS2068, "Bare Metal" Pi, Next KS2, IF1/Microdrives/Vdrive/Light Gun/VGA-Joy
QL: Minerva/QL-VGA/Custom PSU
C5: 24v, LiFE battery, Disc brakes
Spinnetti
Posts: 253
Joined: Sat Sep 12, 2020 11:29 pm

Re: TS1500 no video

Post by Spinnetti »

I replaced the 2 power transistors, so that wasn't it - no change in voltages.. seems like next logical thing to check/replace is the diodes in the power circuit?
Zeddy: ZX80, ZX81/ZXpand, TS1000/ZXpand, TS1500/Zxpand+
Speccy: 48k, +, +2, +3, TS2068, "Bare Metal" Pi, Next KS2, IF1/Microdrives/Vdrive/Light Gun/VGA-Joy
QL: Minerva/QL-VGA/Custom PSU
C5: 24v, LiFE battery, Disc brakes
dessony
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Re: TS1500 no video

Post by dessony »

Spinnetti,

Are there any of the 4 electrolytic capacitors looking like some kind of cucumbers within the DC-DC converter circuitry? These capacitors might fail without your knowledge. Test these capacitors for ESR. I concurred with 1024MAK. I also quoted this sweet gentleman on these capacitors.

DesSony
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