My SA - 7100 Drops in and out of Protection

I really cannot understand what went wrong.
After meticulous planning and preparation, careful solder work, replacing items on by one.
I was confident all the way, and in the end I just got the dbt wrong. I don't know what made me think the opposite.
What went wrong with my amp ?
 
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Hi Pat, good to know your still around for this.
Yeah, I did take a break from this to reset my brain.
So as it sits now, it's showing no sign of life. No power light, nothing..
I still can't believe it, after all that work it comes to this.
Where do I start ?
 
Actually I had checked the fuses on the power supply board previously and all three checked out ok.
Then I realised there was the one on the back of the unit. Mine is a multi voltage unit with the fuse holder screwed into the centre. (1a)

It's blown. I have a couple of spares.

So with this, what could have caused it to blow ?
 
the last thing you did was the amp board?

was there any magic smoke/and or strange noises or do you think the fuse just went?

Check your work on the amp board, all transistors ECB are they correct.

Also it may be the trimmers you put in or the settings:

I think you did DC offset @midpoint
And the bias you turned all the way in one direction?
 
the last thing you did was the amp board?

was there any magic smoke/and or strange noises or do you think the fuse just went?

Check your work on the amp board, all transistors ECB are they correct.

Also it may be the trimmers you put in or the settings:

I think you did DC offset @midpoint
And the bias you turned all the way in one direction?

Yes, The Amp Board was the last one..

Ok, I found some issues. I can't believe how I did this either..

Somehow I got transistors mixed up from Q5 to Q10.

Here's what I found:
I put KSC3503DSTU in Q7 & Q8. Should have been KSC2690AYS.

I put KSC2690AYS in Q5 & Q6. Should have been KSC3503DSTU.

I put KSC2690AYS in Q9 & Q10. Should have been KSA1220AYS.

All these have now been corrected.

By the way, there was no magic smoke or strange noises when I powered it up prior to this. The fuse blew immediately after the protection relay clicked.

I also checked the output transistors for any shorts. All checked ok. I followed a reliable test procedure i found on you tube.
http://www.youtube.com/watch?v=REW2lF0sb74

All transistors are correct in terms of pin placement. The TO-126 are all ECB.
Pin 1 being the 1st on left on the printed side.

As for the trimmers, I do recall setting these after pulling them from the board to the correct spec, then re soldering them in. The pin placement on these I am sure are correct, but feel free to scrutinize these from the pics provided previously, and data sheets from the links below for each.

VR 1, VR 2 (4.7K): 652-3296P-1-502LF
http://au.mouser.com/ProductDetail/...=sGAEpiMZZMvygUB3GLcD7n4W/LGLppVQAt4Gicko0hk=

VR 3, VR 4 (100ohm): 652-3386H-1-101LF
http://au.mouser.com/ProductDetail/...=sGAEpiMZZMvygUB3GLcD7rufck0TIBKy/8deGTAIvjY=

I'll await further instructions.
Thanks for your patience.
 
ok so now that all the transistors are in the correct positions bring up on the dim bulb. The bulb should at turn on glow bright and then quickly go dim. If that is the case you should be good to turn on and do the amp settings. If it is turned on and bulb glows bright and stays bright we still have a problem.
 
Ok thanks.

I'm just getting ready for work, I'll try and get back to it this afternoon.

Also, I forgot to mention. All the while I had wires 1,2,3 & 16,17,18 disconnected in previous dim bulb and power up.
At what point should these be reconnected (soldered) ?.
 
Trace Question.

By looking at the pic provided, the trace for the emitter on Q9 transistor on the Amp board had some of the foil stripped where the pins comes through, but I managed to solder in most of the pin to the trace.

Qu. Is this still ok ? Will it affect voltage transmission ? Do I need to run a bridge wire to correct this ? If so, where would the bridge wire go ?
 

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Did you check with a DVM for continuity? It is hard for me to see if you have a solid connection there by that pic, I hate when a trace pad lifts. If you run a jumper it would go to another pad on that trace, I see 2. You would need to desolder both and then run the jumper between.





By looking at the pic provided, the trace for the emitter on Q9 transistor on the Amp board had some of the foil stripped where the pins comes through, but I managed to solder in most of the pin to the trace.

Qu. Is this still ok ? Will it affect voltage transmission ? Do I need to run a bridge wire to correct this ? If so, where would the bridge wire go ?
 
No Cigar

I tested those traces as you mentioned. Continuity confirmed.

After powering up on dim bulb this morning, I started out with a 60w globe as i did previously. At first, the light dips slightly then brightens only marginally. Didn't get as bright as it did on previous occasion.
Then I thought I'd try a 100w globe to see what happens.
Starts off dim, click of the protection relay and bulb stays relatively dim.
Something unusual though. The inner main filter cap (Panasonic CE THA) gets noticeably warm while the outer remains cool. The inner one has now a slight bulge and I could hear a fizzing sound from it internally. Sounds like it's cooking up somehow ??
:confused:
 
capacitors fail with ....
1 age
2 over voltage
3 connected wrong way round
4 ac volts across a dc capacitor .
 
All was well until you got to the amp board. Are your wires still disconnected to set bias?

Here are my 7100 amp board before and after, lets go over this.




 
All was well until you got to the amp board. Are your wires still disconnected to set bias?

I've checked all transistors again and all are the correct items.

Yes, the wires are still disconnected, though my main concern is that one of the Main Filter caps has a slight buldge from over heating as I mentioned before.

If I set about to adjust offset and Idle current with this problem it can only make it worse. After powering up on DBT previously, It was only on for around a minute or so and I could hear it fizzing up inside and getting very warm to the touch. The one next to it was cool and didn't have the same symptoms.

I'm afraid it may explode. Do you think it will ?
 

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What could be causing only one filter cap to overheat ?

Is is possible the problem lies elsewhere other than the amp board ?

I never powered up between stages to confirm any work. It just happened to be that the amp board was the last one I did and none were done in any particular order.
 
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