Lexel 88 problems - Help please

[smogthemog]

Some pics from todays proceeding:

[mixedgas]

[QUOTE=smogthemog;142299]By R2, do you mean the 2K 25W resistor?

Yup. That one. Never seen a case where 50% of the semis on the CPC are fried. Nearby lighting strike?

Better really check the passbank rectifiers, like place them in series with a 100 watt lightbulb or something outside the psu. Please also check the big lytic by charging it.

Mental note, incandescent lightbulbs for troubleshooting and load limiting on old radios etc while trouibleshooting are soon gonna be bye-bye. I better buy a few packs...

God must want you to keep this laser, because he sure is getting you the master course on troubleshooting it. Very few ever get as bad as this one. Usually its just one or two small parts and your back in business. Lexels are VERY reliable when ran within parameters..

Hey, the fact that several of the resistors on the CPC are carbon instead of 1% metal film suggests its been worked on before, perhaps by a insidious ham handed tech? You almost NEVER need to replace resistors on the CPC... Hum, methinks it took a big hit or a big miswire... Looking at that molex connector hanging by the current pot, it looks like this one has been modded. Then looking at the light card, it has a specialized OEM light card that the molex goes into.
Since nearly everything is at B+ or B- in the PSU, except for part of the light card, you have to watch when using line powered instruments or hooking up external gear to the remote jacks. I assume K8 has been modded so you can fire it up without needing a external 24V? Other then the different light card and the newer style filter inductor she looks normal, more like a 88D then a 88A, and 88Ds are rated for a bit more power, in fact there are very few differences between a A and a D.

Excellent "upskirt" photography, can we have a modest shot of her face please..... I want to see what test points and what metering you have ,... Your also missing one fuse holder on the rear...

BTW, is the fuse between the light/current switch and the passbank fried? Its supposed to protect the CPC by blowing the opamp and the fuse if the bases become reverse biased some how...
(I'm thinking its called F4)

I'll try to scan in the real drawings asap.

Wondering when Buffo is going to contribute to this thread...

Steve

[smogthemog]

Just off to work now Steve so a bit pressed for time but I took a few shots of the cards, the light sensor (which is broken ), the Igniter and a few more external & internals.

I haven't checked the fuses yet - MY BAD Should have been the first thing to check!!!!

Just waiting for the components to turn up now and this, which I treated myself too:
http://uk.farnell.com/peak/dca55t/an...lue/dp/3727476

Should come in handy

[mixedgas]

Years ago I treated myself to one of these:

http://www.web-tronics.com/lilbittytester.html

OK, R7 and R10 on the control card do not look factory....

Steve

[smogthemog]

Having a little problem getting the MPS 6534 and 6531 transistors and can't seem to find any equivalents. Do you know of anything to match them Steve?

I am going to fit the 6295's this evening and check those Caps, Oh and that resistor and fuses you mentioned.

Having 2 ankle snappers dosent leave me much spare time to concentrate on it but I MUST get it done for the impending LEM

[smogthemog]

Having a little problem getting the MPS 6534 and 6531 transistors and can't seem to find any equivalents. Do you know of anything to match them Steve?

I am going to fit the 6295's this evening and check those Caps, Oh and that resistor and fuses you mentioned.

Having 2 ankle snappers dosent leave me much spare time to concentrate on it but I MUST get it done for the impending LEM

[mixedgas]

[QUOTE=smogthemog;142394]Having a little problem getting the MPS 6534 and 6531 transistors and can't seem to find any equivalents. Do you know of anything to match them Steve?


2N4401 works for the NPNs. 2N2222 can work in a pinch but I do NOT leave 2n2222s in the circuit unless they are the metal can package...

As for the PNPs... selected high quality 2N3096 or other 500 mW PNP with similar beta and Vce.

Steve

[smogthemog]

2N4401 works for the NPNs. 2N2222 can work in a pinch but I do NOT leave 2n2222s in the circuit unless they are the metal can package...

As for the PNPs... selected high quality 2N3096 or other 500 mW PNP with similar beta and Vce.

Steve

I have found a 2N4401 scource but getting a 110A SCR come back as a 2N3096? Is that the correct number Steve or is it a 2N3906?

EDIT - I guess it was a 2N3906 cuz that seems a very close match. I have ordered some 2N4401's and 2N3906's to get me going until the MPS's arrive - they may be a while as they where out of stock
FYI - The 0.5A SB fuse at the rear was blown!

I have started fitting the PB TX's tonight, I also checked the diodes in the bridge rec - they all seem OK.

Thanks again for your help

[smogthemog]

I got the transistor checker today and whent through the 2N6295's with it. I have the following Hfe readings from the 12x transistors:

9
11
32
26
22
22
12
8
19
4
14
20

Are they good enough to be anywhere near 'matched'? bearing in mind I didn't buy a matched set My Bad!

I also got the Zeners and the 1N457's which I will be fitting later tonight. I can then check the voltages once again on the card.

I also checked all the MPS TX's and apart from 2 of them, one was short and one had a very low Hfe reading (55, where the others are all 130+), the other all seem OK and are to spec.
I will replace the two with the 2N's that I need to replace and leave the rest as the MPS's.

Which do you think Steve would be the safest of the 6534's to replace with the 2N's?

[mixedgas]

[QUOTE=smogthemog;142517]I got the transistor checker today and whent through the 2N6295's with it. I have the following Hfe readings from the 12x transistors:

9
11
32
26
22
22
12
8
19
4
14
20

I'm at work, no time to type.
clip the "4" from the circuit. The passbank will easily run with 10 transistors, 11 will be fine.I'll get back to you on the rest when I am done with the current crisis at work.

Steve