Wells Gardener 19V1001

[Ronnie Dent]

Now you should measure the base - emitter voltage of Q204. Base should be 0.7V higher than emitter. If that's the case, Q204 is probably defective as it's collector voltage should be lower.

If it's not the case, the voltage divider being R214 R278 R213 R212 R211 could be having a problem, but I put my money on Q204 for the moment. If you adjust R212, collector voltage should change. Base emitter will be constant as transistors are current driven.

Sorry it was Q204 I measured above base was 33v as was emitter? do you mean across base emitter rather than ground?

Thanks Ronnie

 

[obcd]

Yes, that's what I mean. As the difference is less than a volt (0.65 - 0.75) under normal operating conditions, you might have missed the little difference between the 2 voltages. Normally there should flow a current between base and emitter, and that should pull the collector voltage down.

If you don't have the voltage difference, you can remove that transistor and measure the base voltage with it removed. If you measure Base emitter of the transistor with your meter at diode test position, it should read infinity in one direction and 0.5 - 0.75 in the other. If it measures as a short, the transistor is bad. Maybe you have a hfe tester on your meter to test transistors?

 

[Ronnie Dent]

Ah sorry I misunderstood.

Base and Emitter voltages are slowly creeping up emitter was at 33.69 and base 33.84 after a few seconds. I have a cheap transistor tester so I will remove Q204 and test it, I'm hoping the new MPSA06's will arrive today

Thanks Ronnie

 

[Ronnie Dent]

Just noticed the the MPSA06 I ordered says they are PNP? but the manual states they are NPN I thought that part number would all be same polarity?

these are what I ordered

http://www.ebay.co.uk/itm/261633822582?_trksid=p2060353.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Thanks Ronnie

 

[Ronnie Dent]

Also I removed Q204 it reads B to E 6 ohms either way so almost short? I'm confused on the PNP NPN as I see both types listed on Ebay as MPSA06?

Thanks Ronnie

 

[obcd]

MPSA06 should be NPN and MPS56 is PNP.

I think the seller made a mistake in his announcement.

You could contact him and ask about it.

 

[Ronnie Dent]

MPSA06 should be NPN and MPS56 is PNP.

I think the seller made a mistake in his announcement.

You could contact him and ask about it.

Thanks, confusing but I'm easily confused! I will as him the question.

The result for Q204 I think it's bad 6 ohms Emitter to base either way, if so you were right.

Thanks Ronnie

 

[obcd]

Indeed, that Q204 looks pretty bad.

It's better to be confused and to double check things than to assume it will be correct.

 

[Ronnie Dent]

Indeed, that Q204 looks pretty bad.

It's better to be confused and to double check things than to assume it will be correct.

Yes that's true, thanks again hopefully Q204 will be the culprit, no new transistors here yet but the seller confirmed the listing was wrong so that's good.

I wonder now on the other chassis why the B+ would only be 37v? it might be worth the time to fix up this spare chassis as apart from dirt it looked in good condition.

Thanks Ronnie

 

[obcd]

For dirt, use an air compressor and blow it away. Vacuum cleaners suck for this kind of work.

I would try the supply with the 60W load first. Maybe there is a short on the chassis (like the HOT) that pulls the B+ voltage down due to overcurrent. You might measure the HOT transistor and check if it isn't shorted. Other candidates for a short are the vertical deflection coil driver transistors. You could try the chassis with the HOT removed, as the wire trick you used on previous chassis won't remove the short if it's the HOT. Even with a defective voltage regulator circuit, I doubt the B+ would go as low as 35V. You could check that on the other chassis by removing Q 101 (at least that's the number I think)

 

[Ronnie Dent]

For dirt, use an air compressor and blow it away. Vacuum cleaners suck for this kind of work.

I would try the supply with the 60W load first. Maybe there is a short on the chassis (like the HOT) that pulls the B+ voltage down due to overcurrent. You might measure the HOT transistor and check if it isn't shorted. Other candidates for a short are the vertical deflection coil driver transistors. You could try the chassis with the HOT removed, as the wire trick you used on previous chassis won't remove the short if it's the HOT. Even with a defective voltage regulator circuit, I doubt the B+ would go as low as 35V. You could check that on the other chassis by removing Q 101 (at least that's the number I think)

Yes I have a good air compressor for that job, on the other chassis it looks like Q101 reads very low ohms from it's case to one of it's pins so I think that is bad, I will wait until the new components arrive and maybe I can see if it will work properly with the new Q101 fitted, I hope these will be delivered tomorrow now.

Thanks Ronnie

 

[Ronnie Dent]

Just received the MPSA06 transistors and quickly fitted one to Q204 and I'm happy to report a B+ at 77.8vdc, but I can't get it any lower on the bench? maybe because load is not heavy enough for a voltage drop? otherwise all looks good, many thanks again obcd for stepping in to help, and this is not the first time he has offered to help me either. I'm sure others will find the tech help in this thread very useful as lots of old Midway games had these chassis, Boot Hill, Break out, space invaders to name a few.

Thanks Ronnie

 

[Ronnie Dent]

Can you confirm B+ being 77v as being okay as it will not go lower on the bench but I can increase it no problem so the pot etc are working?

The replacement Q101 transistors have not arrived yet but hope to have the spare chassis working also but not a priority

Thanks Ronnie

 

[obcd]

Sorry, ddidn't check the forum for a while.

If it adjusts up to 77 you might reconnect the tube and see how it goes with that. You will probably be able to adjust it down to 75V which would indeed mean that your load is a little 2 small.

And hopefully no wobble anymore.

 

[Ronnie Dent]

Sorry, ddidn't check the forum for a while.

If it adjusts up to 77 you might reconnect the tube and see how it goes with that. You will probably be able to adjust it down to 75V which would indeed mean that your load is a little 2 small.

And hopefully no wobble anymore.

No problem, thank you, yes fingers crossed no wobble! we away for the weekend so will be Monday before I can test it but will report back

Thanks Ronnie

 

[Ronnie Dent]

Happy to report this chassis is fixed, back in the machine voltage dropped to around 60v adjusted it up to 75v no problem and I have a nice wobble free picture. Not got the game board but I connected one of those multi game sticks that takes batteries and the image is fine.

Also the other chassis which had a 37v B+ I fitted the other Q101 I ordered and on the bench it's now sitting at 74v but the pot is not altering that voltage? I'm sure I could go up on the other chassis so maybe another fault?

Thanks Ronnie

 

[obcd]

If you can post some voltage readings. (with the adjustment fully clockwise and fully counterclockwise), we might be able to figure out what else is wrong.

 

[Ronnie Dent]

If you can post some voltage readings. (with the adjustment fully clockwise and fully counterclockwise), we might be able to figure out what else is wrong.

Hi thanks, it does not alter either way up or down it stays at 74.5v, this is with the the 60watt lamp connected to B+ also no capacitors have been replaced yet

Thanks Ronnie

 

[obcd]

I understand, but maybe the voltages around the 3 transistors change when the potmeter is adjusted?

 

[Ronnie Dent]

I understand, but maybe the voltages around the 3 transistors change when the potmeter is adjusted?

Ah I see, Q101 102 and 104, I will check thanks