| 745 PA - SEARCHING FOR PCB COMPONENT LAYOUT [message #29372] |
Thu, 28 November 2024 22:06  |
Voxman2027
Messages: 9
Registered: November 2024
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Junior Member |
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Hello ONE AND ALL
I'm currently working on my first Kustom amplifier and seeking out a component layout sheet if one exists. I've looked on here for one but all I've found are the schematics. Only one link does anything ... the rest are dead-ends.
Having a component layout would really help navigate the circuit. Several times in the past I've actually took photos of a PCB and then meticulously and tediously identified every part on PCB. Those were smaller circuits so not too difficult to do. However this amp is a lot more complicated so it will take me some time to label all the components.
So hoping I don't have to...
And while I've got anyone's attention, I am troubleshooting no output although amp appears to be operational. I've resoldered a capacitor that had come loose, reattached the output transformer that was loose, replaced the 2 final output transistor for fun ( one was getting warm without signal, so I thought why not replace the pair - I installed sockets for the transistors so I could easily remove/replace if necessary without soldering.) Also removed death cap and installed proper 3 conductor AC power cord. Also cleaned the crud out of chassis that looked like it was kept in a chicken coop.
I've got +38vdc/-38vdc on power rails. So far I've traced the signal through the first transistor but it's been difficult trying to figure out where the signal is supposed to go next. Hence the search for an accurate pictorial component layout diagram. There's only 3 wires coming off the preamp input PCB and one goes to reverb PCB, another red wire is the supply voltage and I assume the little blue wire must be the signal wire (nothing no signal here).
I enjoy tracking down this fault and find it relaxing and satisfying when discovering problem and correcting it.
Thanks in advance for any help, advice or suggestions!
Best regards
Gary
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| Re: 745 PA - SEARCHING FOR PCB COMPONENT LAYOUT [message #29388 is a reply to message #29372] |
Sun, 08 December 2024 23:10  |
chicagobill
Messages: 2011
Registered: April 2003
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Senior Member |
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I have never seen a parts layout for Frankie heads.
You can take whatever approach you would like to use in fixing the amp, but I always recommend that you fix the main problem before replacing parts that you just want to replace.
I have fixed close to 100 Frankies and I find that best start to the repair is to get the schematic out and start comparing voltages. When you find that a voltage is missing or really off value from the schematic,, it will lead you to the problem.
You said that the driver transformer was loose, did you check the windings for continuity when you remounted it?
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| Re: 745 PA - SEARCHING FOR PCB COMPONENT LAYOUT [message #29391 is a reply to message #29389] |
Mon, 09 December 2024 12:49 |
chicagobill
Messages: 2011
Registered: April 2003
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Senior Member |
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There are 6 TO-3 power transistors that are mounted on the rear panel. 4 are the output transistors, one is the driver transistor that feeds the driver transformer and one is the pass transistor for the 24 volt regulated power supply.
The pass transistor usually gets warm as the amp is on, but none of the other power transistors should get hot unless the amp is driven hard for a few minutes.
Do you have a light bulb limiter?
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| Re: 745 PA - SEARCHING FOR PCB COMPONENT LAYOUT [message #29414 is a reply to message #29372] |
Fri, 10 January 2025 06:03 |
stevem
Messages: 4792
Registered: June 2004
Location: NY
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Senior Member |
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If you ever have a next goaround with one of these take note of what Bill posted that will make your troubleshooting easier.
The amp does not have 6 output transistors, but it does have 6 of the same T03 type transistors.
4 are output
1 is the driver to the phase splitter / driver transformer.
1 is the + 24 volt regulator to the preamp( s).
These early amps have no protection circuits for the output stage so if you only play at home and not too loud I would suggest changing out the 8 amp speaker fuse for a 5 or even 4 amp fuse.
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