[KCMike]

I'll give that a try. I broke one pin trying to cross and align/adjust to hole. I do have one extra The mouser electronics has the 2N3704 with correct pin out. the link you put up shows that as a replacement for 2sc905. I will order a few of them unless you think one of the other recommended replacements is better. Thanks

[morzh]

OK.

When working with chips and transistors with plastic bodies, if you try bending pins keep in mind they have that depression (thin part) right where they go in the body, and trying to bend them there often results in breakage or degrades the pin's strength.

The proper way of doing this is holding the pins with needle-nose pliers below those depressions and then bending pins using a second pair of the pliers. Worst case if you break one you will still have a stub to solder to.

Do not bend with your hand and close to where the pins go into the body.

[KCMike]

I was able to turn transistor around and just bend the one base pin over then I put insulation on and installed.
Went ahead and finished the power unit everything else went well.
Starting on amplifier unit next. Thanks for your continued help and advise.

[KCMike]

Well I finished the main amp. board finally after waiting on order for mica insulators for power transistors and holiday duties.
Reinstalled the power and main amp .boards. I brought it up on the variac and at 50 volts it was drawing over 1 amp. I figured if I continued on it would have blown the fuses in the main amp.
Just to recap the begining when I first got the receiver the 2- main amp board fuses were blown. Replaced and powered up it immediately blew the main line fuse.
I then went ahead and rebuilt the power and main amp. checked the power transformer and it tested good.
I unhooked the B+ to the main amp. repowered and it came up fine with ampers reading around .1 took voltage readings of the power board.
Here are the voltage readings from the board.( secondary of the power transformer)
AC-1--59 V
AC-2-33 V
B-1--80 V
B-2--37.6 V
B-3--23.03 V
B-4--21.60 V
B-5--12 V
I have checked an rechecked the transistors for correct placement and that the power transistors are correctly installed with mica insulators and used heat sink compound. went over the traces on the boards looking for any breaks or solder over run all looks good made sure the collector case and bolts of power trans. were not shorting to heatsink. Checked all the resistors and found none open or way off.
I then discovered that the 2-transistors on power supply unit Q1 and Q3 were getting very hot to the touch. This was with main amp still out of circuit.
Went ahead and unhooked the head amp unit B-3 on board (W21-001) from circuit and Q1&Q2 on power unit felt slightly warm. Re hooked B-3 and the Q1&Q2 started getting very hot again.
Sorry for long post but felt anyone willing to help me with what to test next would need this info.
Thanks.

[morzh]

B1 and B2 are WAAAAAAAAAAY different. See what loads it.

Also:

Since it takes time to figure what goes where, can you simply write which voltage from power supply goes where to the boards and if the name changes, then how?

[KCMike]

Thanks morzh. I think this is what your asking for. according to schematic:
B-1- suppose to be 65V. goes to the Main amp with the 2200/80v filter E- cap. I did try another cap to make sure it wasn't shorted and it wasn't.
B-2 - suppose to be 40v goes to Control ampl. unit.
B-3- suppose to be 25v goes to Head ampl. unit
B-4- suppose to be 18v- a red wire. goes to an E-cap on a solder strip positive side. then the neg. of the e cap black wire goes to head ampl. board then to to ground.
B-5- suppose to be 12v goes to Switch -1 also the FM MPX unit ties into it and the AM tuner unit.
Here is the voltages I got so you don't have to keep going up and down post.
B-1-80v
B-2-37.5v
B-3-23.04v
B-4-21.60v
B-5-12v

[morzh]

Mike

Since there are no DC amps in this device, I think it is safe to disconnect every single amp, pre-amp and such and measure unloaded Power Supply voltages and then start connecting units one by one, measuring voltages every time.

What you want to see is at what point the voltages become wrong and things start heating up and blowing fuses.

[KCMike]

I will do that and post the results.
Do have one question. When you say there is no DC amps in device I thought the bridge diodes on the power board unit convereted the ac to dc and that became the B+ that went to other boards? Know that I'm not challenging you. I just want to learn as I go along. Thanks

[morzh]

OK

B5 ( Q3 emitter output) should be about 13.3V
B2 (Q1 emitter) should be 41.65V

Others cannot be calculated as they are dpendent on loads.

[morzh]

DC amp meand an amp that amplifies DC. Those with bipolar supply are usually such.
In your case the mps are AC (they are POWERED by DC).

AC amps when signal is not present do not affect each other and so any unit can be unplugged without worrying about the rest's DC mode etc.
(not while hot though, never a good idea).

[morzh]

Last thing: the B1 and B4 volages can potentially be loaded to blow fuses, the rest cannot. You can low power transitors but not fuses.

[KCMike]

Thank you for explaining that. I will get on with the testing in the morning and post it. Long day and shouldn't do any work tonight. If you think of anything else I should do let me know and I will check here before testing tomorrow.

[KCMike]

I hooked every thing up except the main amp B+ wire.
Powered up with variac to 115v. Every thing seemed fine.
I took voltage measure on dc reading. B5 , Q3( B to E .660v) (E to chassis ground .867v) ( C to grnd 12v)
B2,Q1( B to E .608v) ( E to grnd. 4.06v).
I turned off and hooked up B+ to main amp. powered up on variac at 50v was reading over 1 amp. problem still here.
I unhooked main amp and started rechecking volts as I removed each unit from power board. B2 control amp and B3 head amp unit seems to have a problem.
When either B2or,B3 are hooked up the volts on B2 and B3 drop to 14volts from 38v. I'm measureing at the posts on power board. B2 andB3 are also reading the same 38v or 14v B2 is supposed to be 40v and B3 25v.
I hope I explained this clearly enough.
Wondering if I will have to rebuild head amp and control amp. I don't want to get ahead of problem by guessing.

[morzh]

Can you hook up main amp one channel at a time or the two are hardwired to each other?

[morzh]

B2 should not drop when connected, it is regulated and it means overload, B3 can dop, but depends on the load.


Have you checked ALL. the transistors in the Main amps?