Lexel 88 problems - Help please

[smogthemog]

Card testing.
remove LM301.
Connect a set of test leads to circuit specialists PSU. Set PSU to max voltage. short leads. Adjust PSU constant current mode to 100 mA indicated. Unshort leads. connect ground to ground on card at pins 19 or 20. Connect B+ from PSU to Of couse with that PSU (18V version?) you may even get close to turning on the +30V or the +20V zener, but you should see the other voltages and the neg rail. adding a 9V battery in series with the PSU would get you 27V and you might see the 20V zener start to clip.
(remember this must be current limited some how) So you should see +15, some negitive voltage etc. What you get depends on how good your inverter circuit on the board works.

Steve

I did this as you said earlier in the thread but you didn't mention removing the LM301

The PSU is 30V but will go to 32V and yes the 30V zener is begining to clip at that voltage.
I have the +/- 15 & 20v rails and also the +6.2v rail.
I took out all the transistors, I then applied the 30V to the top of Z1 and ground. At Z2 I had +20V and at Z3 I had +15v. I then powered down and replaced Q2, 3 & 4 then powered back up again. I then had the -20 and -15v rails.
After fitting Q1 I then got the 6.2v on Z4.

Considering 2 of the zeners had blown I am going to change the LM301, when it gets here, more so as a precaution. I have then checked and mostly replaced all the semiconductors on that CPC board.
The 2x non OEM resistors you mentioned are both OK and to spec.

I will be performing the live tests on the PSU another night - Bit strapped for time tonight.

I now have a source for the MPS 6534 and 6531 transistors but am not going to order until I have tested without them as there is no point in spending more money if the 2N4401's and the 2N3906's will do the job.

Shall I remove the 1-2 second glass (valve style) timer relay so that it dosen't try to ignite the tube when I do finally power everything up?

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Sorry to sound a bit fik but I could do with some clarification on a few bits Steve?

Disconnect psu from line voltage. OK
Set taps per chart I sent you. OK
CAUTION, LETHAL VOLTAGES PRESENT! OK
reconnect line power. OK
close breaker, do NOT press start, OK
I. confirm line neon lit. OK

II. Check "AC" test points with volt meter, shoud be some place between 110 and 133 volts.

IF NOT< STOP> Should be NO dc across cap. If there, is, bad contactor, stop. OK

Now set meter switch to reg volts OK

Press start. OK

III. Massive THUMP from contactor closing. OK

IV Breaker cooling fan should start and run smoothly. OK

V. Power neons (2) lit and stable. OK

VI, NO smoke. Nope, no smoke

VII cap should rapidly start to charge, with massive surge. OK

VIII. Low AC ripple across cap (most modern meters CAN look at AC sumperimposed on DC, use 110V ac scale, but check meter manual, may be a volt or two or three residual ac, but any massive amount of AC means BAD cap) Meter will do this.

VIII no reg volts reading If reg volts more then just off peg from leakage, power down straight away. OK

VIIII switch to amps. NO amps flowing IF amps flowing power down. OK

X. Switch to DC volts, should match open circuit V on cap +/- 5% or so. OK

XI, Open circuit voltage unloaded should be around or greater then 1.414 times the AC voltage from the buck/boost autotransformer. Do note it is a autotransformer , not isolated, and may act a bit strange when unloaded. OK

XII cathode transformer unloaded should be in the greater then 3 volt region and the voltage should change a small amount as you change the cathode switch. Power down main breaker before changing switch. OK

115NO30 relay should require about 30 seconds to time in. OK

Pin P (anode) to either of the cathode leads should be the same as the DC cap voltage. OK

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Thanks again for your inpresidented help Steve - your da man!!!!!

[smogthemog]

A few photo's for prosperity and to help others if need be

Oh and a couple of my little son, Toren, that crept in there

[smogthemog]

I did all you said last night Steve and it all seems OK.
I am getting 34V and meter reads 31v so thats not too bad.
0.012v AC ripple across the cap.

Just got to get around to replacing the LM301AH, which I now have, and I will be giving it a spin

[mixedgas]

Where are you getting 31 volts cold with no plasma? On the zener? You should not SEE anything with the tube off on the meter except 250 something DC open circuit, it then drops to the tube voltage...

SOMETHING IS STILL WRONG

Steve

[smogthemog]

I get the 34v between TP2 & TP3 from the front panel with my Multi Meter attached and also on the panel meter when it's switched to REG volts.
I get it when I switch on the line breaker, defeat the interlocks and then press the start button BUT before the 30 second timer times out. I actually removed the timer so it didn't time out because I didn't know what it would do??

[mixedgas]

Something is conducting that should not.

Should be near zero across the passbank if its off.

Steve

[smogthemog]

This is without the card out, head disconnected and with 230V connected.
I haven't replaced the 60V 5W zener yet?

There is a 30V rail from the cold end of R2 which will be live as soon as the start switch is pressed, could it be this I am reading Steve? But if so, how?

There is deffo 34Vdc between TP2 & 3 and 272Vdc between TP3 & 4

Shall I see what happens when the 30 second timer times out or will that be too risky?


EDIT - I have just replaced the zener and it's still the same

[smogthemog]

I have just noticed that R1, a 25W 5K resistor has been replaced with a 25W 3K resistor.

Could this be anything to do with it?

I have checked C2, R4, R6, R31, R5, D1, R2 and replaced Z1 and D6.

I also checked the voltages between TP1 and the Emitter side of each of the 2N6259's and got no volts on any of them when switched on.

If I de-solder the base connection on Q1, the small PB driver, that 34v rises to 40V??

If I put my MM between TP2 and TP3 I get 34v if the meter range switch is set to Reg Voltage and 60V if it is flicked over too the Tube Current range?

I am really struggling here as I am limited in my electronics knowledge and I just cannot see what is wrong if you say there should be zero volts here

[mixedgas]

Lift R32 and see if that voltage goes away. If it does, reconnect it, and your ready for testing. If it does not, you still have a problem.

You've done fine on the diagnosis/repair, most people would have never gotten as far as you have now.

Steve

[smogthemog]

I will give that a go Steve, Thanks.

Jim