CA-1000 Rebuild Issues

[jandajr]

Before I get into this test, I thought it might be a good idea to get some spare parts. Just in case.

When I rebuilt the Main Amp boards:
I used KSC2690AYS on TR604, 605606. Would KSC2690AYSTU have been better?
On TR602, 603 I used KSA1015YTA
On TR606, 607 I used KSC1815YTA
On TR608 I used KSA1015YTA
TR601 / SK30A-GR I didn't replace, I wasn't able to locate an equivalent. Is there one? Luckily it tested OK.

 

[avionic]

I used KSC2690AYS on TR604, 605606. Would KSC2690AYSTU have been better?

AY-S versus AY-S-TU -- electronically identicle..
Difference is packaging..
AYS would be loose parts in the bag.
AYSTU parts are shipped in a plastic TUBE..

 

[bobdod]

TR601 / SK30A-GR I didn't replace, I wasn't able to locate an equivalent. Is there one? Luckily it tested OK.

Interestingly enough, I just replaced two of these on my CA-2000 meter board. Both of them "tested OK" with my cheapo component tester, but at least one was actually faulty, so if you're using a cheapo tester, there could be a small chance that your results are not conclusive. That said, It is highly doubtful that TR601 is your issue, and these fets rarely fail, but just something to consider if you run out of possibilities. OEM replacement can still be found.

 

[jandajr]

I'd try with the diodes alone then DBT power up, if bulb dims ok then try full power up. The 1N4148 is a 1A item so fairly robust.
Connect diodes, TR609, TR611, base=anode, emitter=cathode. TR610, TR612, emitter=anode, base=cathode.

Happy New Year
I replaced the smoked resistors, then placed the 1N4148 per your instructions. Fired it up on the DBT, then under full power for a couples of minutes. Seems to be OK. NO smoke, or pops/sparks. I don't want to assume the next step.
I believe I should add one transistor to the board, and go through the DBT and full power test before adding another transistor and going thru the same process til I find the bad transistor.

 

[mbz]

Plz check some voltages to see if things have normalized.
Measure dc voltages to GND/chassis at TP3, TP4 then the following
points highlighted,
- Wire/point C, and S
- TR611base, TR612base (see pad on component side)
- top then bottom lead of the bias resistor R617
- D607 cathode

 

[jandajr]

TP3 = 0.10
TP4 = 0.10
C = 14.2
S = 51.4
TR611 = 0.1
TR612 = 0.1
R617 = 14.6 Top and Bottom
D607 = 0.1

 

[jandajr]

Under Full Power
TP3 = 0.10
TP4 = 0.10
C = 16.3
S = 53.6
TR611 = 0.1
TR612 = 0.1
R617 = 16.5 Top and Bottom
D607 = 0.1

 

[mbz]

Don't use DBT for the time being.

C and S voltages look totally wrong, maybe a measurement error?
Measuring DC voltages with black MM probe connected to any black speaker post?

Check the orientation of the 1N4148 diodes inserted into the output transistor sockets.
The diodes should be pointing outwards, not pointing to the middle of the board. If you
got this wrong then DBT power up. There needs to be electrical contact between the diodes
and sockets, maybe bend diode legs into a tight "U" and insert the "U" into the socket...


Possibly TR609 has failed b-e open. Diode test the b-e pins, in circuit is ok looking for 0.65

The +50 rail (brown wire) looks high, please measure

 

[jandajr]

Schematic shows C @ 1.15(1.9), S @ 3.9(1.9). Is that correct?
Left channel has C @ 2.4 and S @ 5.1
I'm measuring DC voltage with black MM probe to chassis. Tried to black speaker post. No difference.
Diode Orientation is correct, with tight leads.
TR609/1N4148 B @ 52.9, E @ -5.2
+ 50 rail 52.9
- 50 rail 52.9
Power Supply Board has been rebuilt.

 

[mbz]

Schematic shows C @ 1.15(1.9), S @ 3.9(1.9). Is that correct?

() figures are for Class A. I've measured C at 1.9V and S at 4.5V so in that ball park. Left channel C&S are a little high
probably driven by the higher +50. You might have a small problem in the power supply in the power supply, did you replace
the zeners D703,,,D706.

Under Full Power
TP3 = 0.10
TP4 = 0.10
C = 16.3
S = 53.6
TR611 = 0.1
TR612 = 0.1
R617 = 16.5 Top and Bottom
D607 = 0.1

Above C&S does not make sense.
With +50 at about 53V and point C at 53V means no current flow through R613, R614 so no volt drop however
there is a 53.6-16.3=17.3V drop across R615 (37mA). Possibly you have a solder bridge in the area of wire C
maybe VR603? Maybe post hi-res pix of both component and solder side.

 

[jandajr]

I can't seem to find a solder bridge
I'm going to check D703/706
Thanks

 

[jandajr]

I used BZX55C30 Zener for D703, 706.

 

[mbz]

Zeners D703,,,6 are not the cause of your problem, just that the rails voltage is a little high.

Noticed that you've replaced TR609, TR610 (drivers) with diodes. The suggestion was to replace the outputs/mains TR611, TR612 with diodes. Anyway, it looks like you've got the orientation of diode for TR609 wrong. The banded end should be on the emitter. You may get smoke if you correct this, ie, need DBT power up. Still need to work out why C&S voltages are way out, certainly this diode would block current flow.

EDIT: With amp powered off/unplugged check resistance between wires +50 and S. 53V at S is a concern. Might be due to that TR609 diode orientation.

 

[mbz]

Also check nothing sinister on exposed track and solder joint. Resistance between C&S to be about 470ohms.

 

[jandajr]

I haven't run any more test yet. I want to be sure (test) diodes are correct.
Correct?




I don't see any bad soldering.


Resistance between C&S: Left Channel 474 Ohms Right Channel 22.9K

 

[mbz]

Resistance between C&S: Left Channel 474 Ohms Right Channel 22.9K

Appears R615(470ohms) has failed, remove, retest, replace.

Diodes look ok.
EDIT: Sort out R615 then DBT power up, check voltage at point C.

 

[jandajr]

R615 reads 475 Ohms.
Damn, I thought we had it.

 

[avionic]

C looks like a potential cracked solder pad.

 

[jandajr]

I checked from C to the open pad and found that I had 300+Ohms
Pulled the solder from C, re-soldered and rechecked to open pad 0 Ohms. Great!
Re-measured resistance between C & S same 23K.

 

[jandajr]

474 Ohms at last!
Re-soldered R 615. Now I have 474 Ohms on the Right Channel.
Pulling the solder from "C' and re-soldering both "C" and R 615 apparently did the trick.
Unbelievable.