16mm kodak pageant av-12e6 sound projector

[Osvaldo Flores]

I have a kodak pageant av-12e6 16mm projector that trips the breaker every time I turn on the amplifier switch. The exiter lamp stays on, but of course, no sound from the amplifier. I notice that the 25 Ohm 25Watt resistor on the power supply is getting real hot. Can anybody help me to diagnose the problem?
(I attach the schematic of the AV-126-TR that is the only one I could get) Thanking in advance to anybody that can help Kodak AV-126-TR schematic.jpg

[Jim Cassedy]

I worked for an authorized B&H & Kodak repair center for a while in the mid 1980's.
I never really liked working on these particular Kodak machines. But I do remember
there was one transistor in particular that seemed prone to failure, resulting in a
tripped circuit breaker. Unfortunately, I don't really recall exactly which one it was,
except it was one of the 'big ones' in the TO-3 type package. It was part of a pair,
and if one went, we usually replaced both of the pair. The TO-3 transistors were in
sockets, so it's relatively easy to pull one out and test for a direct short it with a
meter or transistor checker. So I would start with those since they are easily
removed. - - but you're going to need some new thermal grease when you put
the back. I also seem to recall that Kodak used some really cheap stuff which
was also pretty messy. We always suspected that the transistor failure may
have in part been caused by the cheap thermal grease they used. Good Luck!

[Osvaldo Flores]

Thank you very much for your quick response Jim, I will start checking this 2 transistors .
Osvaldo

[Mark Gulbrandsen]

They do give you voltage readings on your schematic, so you can also check those for a hint at what is wrong.

[Osvaldo Flores]

Thank you Mark

[Stefan Scholz]

The 25 Ohms/ 25 Watt watt resistor will get hot, there is a reason it is a 25 W taype, to dissipate heat. That's not the fault, it limits the current through the exciter bulb. A very bad design, as is uses the power amp supply voltage. It's pure energy waste.
Most likely it is a fault in the output transistors. (Q7/Q8) are TO 3. I doubt C13 will be shorted out. These are the only components which can lead to a short circuit current able to trip the breaker/ fuse.
Check the main capacitor, then remove the power transistors and measure with a DMM diode test setting.
Then check output on position K without power transistors in place, which can be done with higher impedance headphone. If sound plays, and voltage to ground/ positive is around - 14 to 15 Volt, the circuit is oK.
Looks like this is very old Germanium type transistors. So to source NOS ones can be a little tricky.

[Osvaldo Flores]

Thank you so much Stefan for your help, I really appreciate your input.

[John Eickhof]

They do give you voltage readings on your schematic, so you can also check those for a hint at what is wrong.

Mark, wouldn't that be difficult as it trips the breaker on power up?

[Mark Gulbrandsen]

Obviously, but that should be an easy fix.

[Osvaldo Flores]

I replaced the transistors Q7 & Q8 with new ones (the TO-3 type) but the fuse breaker keeps tripping when I turn on the amp...and of course, I can not do any voltage measures on the board with the breaker off. There is something else I should do to find the fault?. Sorry to bother again with my questions. Thank you

[Paul Finn]

Do you mean CB-1 in the amplifier trips, or the 120volt main AC panel circuit breaker?? If it is the panel circuit breaker, it would indicate a short in the power supply: T1, rectifiers CR3, CR4. filter caps. If it is CB-1 tripping, it could be a shorted C-13 or CB-1 itself being faulty? In any case, poking around with an ohmmeter on the various components with the power OFF should locate a dead short if there is one.

Paul Finn

[Osvaldo Flores]

Hi Paul,
it is CB-1 tripping. I just detected that the Q6 transistor is shorted ( Emitter to collector) , so I'll find a new one and change it, hope that this will make it work. Thank you so much for your response.