Sansui 1000a trouble

jcon109

Active Member
Just picked up a 1000a, removed the bottom cover for pre inspection before power up with a variac. Found one of the 200uf capacitors and diode burned.

I am concerned about possible transformer or any further damage.
Any Sansui gurus out there had this issue before?

Thanks

JC
 

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Pretty common with the 1000A. That's the 1st section of the Voltage Doubler. Don't even think about powering it up unless you really feel like it's the 4th of JULY, burnging up the unit, and blowing the circuit breaker. Replace both 200uf/350's (they can be stuffed easily) and all the diodes, and snubber caps on the V.D. 220uf/400V is minimum I'd go for value/voltage. Gives you a little headroom.

Larry
 
Great I hope that all is wrong. On the diode, 180v 500 ma correct? Anything special I need to know about them?
 
As for the tuner being off .5mHz you can try this. Check the AM Band for accuracy. If off the same, it's probably the dial indicator has slipped on the string. How to check is quite easy. If the AM Band is dead on, then it's an electrical adjustment.

Between the AM and FM numbers is a LOG SCALE. It's a horizontal line with equidistant marks from below 88mHz to above 108mHz. Turn the dial to the LEFT SIDE until it stops. It should stop right on the 1st mark. If it's off, loosen the dial pin from the string slightly and adjust the dial pin to the mark. Tighten the dial pin clamp sections and then paint with nail polish (preferably AFTER you ask the wife or girlfriend!!!!). NOTE: This is the 1st step in doing an alignment for any analog tuner.
You can do it if one or the other bands is off, but the other bands offset will increase or decrease depending on which way the original ofset is.

Larry
 
Thanks Larry!

Ordered the parts today, will post results. Once it is working and all parts are known good I will do a full recap.

Thanks

JC
 
See that the transformer is OK first.

Please read any high Voltage safety tips given here on AK!

I would disconnect the HV wires from the transformer secondary (one wire goes to the common point between the doubling capacitors and the other one goes to a diode, maybe to a small resistor first) and see that you get about 200 Volts AC across the two leads on your multimeter.

If you still blow fuses, disconnect ALL the secondary wires and see if the fuse blowing stops (or better yet, use the DIM BULB test first).

Mark T. :music:
 
Had two smoked caps and a blown power tube on mine. Took one look at all the spaghetti in the bottom and drove it out to Noah a few days later. Hope things go well for the OP.
 
I have not applied power to the unit yet. I am not sure if the previous owner did but the fuse is not blown.
As far as testing the transformer, I attached a schematic for clarification, Should I disconnect the four wires highlighted and apply power to test the transformer.
 

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I performed a dim bulb test and all seems to be correct. With 100 watt bulb, bright flash then dimmed gradually.
 
Just picked up a 1000a, removed the bottom cover for pre inspection before power up with a variac. Found one of the 200uf capacitors and diode burned.

I am concerned about possible transformer or any further damage.
Any Sansui gurus out there had this issue before?

Thanks

JC

This is a very common problem with Sansui tubes amps and receiver of that period.

all the 1000, 1000a, 500a , au111 ect.
I have repaired quite a number of those with the similar problem.

the filtering multisection can capacitors was shorted.. the Diode and the .0001 paralleled capacitor took all the current to GND..
smoke...

first replace that can capacitor and Diode...

get it to work first then all of the grey electrolictic caps need to be replace too.
 
Success!! Replaced both capacitors and diode and fired right up. I do have one power tube red platting, I would hope a recap or bad tube would solve that or should I look for something else?

Thanks for all the help
 
Success!! Replaced both capacitors and diode and fired right up. I do have one power tube red platting, I would hope a recap or bad tube would solve that or should I look for something else?

Thanks for all the help

The coupling caps are likely bad.

Now that you have verified its working operation, next step is to recap the receiver. All of the electrolytic and paper in oil capacitors need to go.
 
I will get the parts list together, I replaced both the diodes connected to the 200 uf capacitors with 1n5408 as per Larry, There is one more round black diode left that I did not replace on the 32 v power tap, can I use the 1n5408 for that one as well?
 
You can use a 1n4004 there. it's a 400V 1A diode. I get my diodes in Bulk so i used a 1n4007 (1000V 1A). The 32V tap is used mainly for the BIAS voltage and a couple other low voltage applications.

Swap the tube pair front to back and see if the redplating stays with the socket or swaps with the tube. If it stays, it's the coupling cap, if it moves with the tube it's the tube.

On the Sansui DO NOT go UP in voltage on the output couping caps. The .33uf 400V caps are tight enough. .33uf 600V or 630V caps will be physically too big.

ALL OF THE ELNA PIO (under 1uf) caps MUST GO! They have a nasty tendency to act like firecrackers and spew paper all over when they go. Replace with good quality Films and you'll be ok. I used Cornell Dublier DME's @ 400V in most places due to size and lead length. Orange drops are twice as big in most cases. For electrolytics UKL series Nichicons work well with TVX series for the axials. DON'T MESS with the MULTIPLEX board.

The transistors in the phono board (under the cover next to the antenna) are Germanium. I haven't found a replacement for them yet.
 
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Just saw this thread and I had a 1000a on the bench with the same blown cap as you originally did. After a full recap the amp is really sweet. Great advice from Larry. Good luck and enjoy it.
 
Well I have this about 90% completed wow what a pain in the a** but it is starting to sound really good. All the little gremlins are slowly disappearing with each step. I am replacing about 4 to 6 caps at a time then testing. Very rewarding work though. Again a big thanks to all the help!

JC
 
Well I have this about 90% completed wow what a pain in the a** but it is starting to sound really good. All the little gremlins are slowly disappearing with each step. I am replacing about 4 to 6 caps at a time then testing. Very rewarding work though. Again a big thanks to all the help!

JC

Yup, major pain to work on. I spent a month doing my 500a. But, it is extremely rewarding - the sound you will get after you are finished is awesome. It makes all the work put in seem like nothing. :D
 
IIRC it took me a month or so to do my 1000A. Mainly problems with the MPX board, which turned out to be a bad (cracked) trace on the board under one of the pots, and you couldn't see it unless you removed the pot.

ONE thing I DID notice on my 1000A. There are 3 - 6AQ8 tubes. 1 for the RF-AMP, 1 for the Muting Circuit, and the last one on the 19kc amp section of the MPX. 6AQ8's are run hard and put away wet. And they avg. $18.00-$22.00 each. The primary substitute for the 6AQ8 is the 6DT8. Avg. $3.00-$5.00 each. The point of all this is that a 6AQ8 is MANDATORY in the MPX. A 6DT8 will not allow the MPX to work correctly. However 6DT8 in the RF-amp, or Muting circuit is FINE.

If you are going to go with NEW STOCK OUTPUT TUBES, I'd recommend the TUNG-SOL 7591 Re-Issues as 1st choice, with the EH7591's coming in 2nd. JJ's come in DEAD LAST! Even below worn out, .22 target old stock tubes. I got a quad of them (TungSols replacing my EH7591's for use in my 800-C's) and they really help the 1000A stand up and smack you in the face. Run them at 75%-80% of Max dissipation (reset the bias to get 14.25W to 15.2W). 19W is max dissipation.

For Example if your Plate voltage is 470V, then you'll need to adjust your bias to between .030 and .032

Divide 15.2/470=0.03234ma Round off to .032
Divide 14.25/470 = 0.03031ma Round off to .030

Use your actual plate voltage and do the math, and adjust accordingly. Mine tend to like the upper end of the settings.
If yours is a single bias pot unit, avg out the quad to .031 (matched pairs are recommended)
If it's a 2 pot, avg the pair out to .031 (matched pair is recommended)
If it's a 4 pot, set each individual tube to where you want.

There is a 4 adjustment board (DIY) that is used on FISHER 400-500C-800C's that works well on the SANSUI. I built one for my 1000A and it works really well. Go to the FISHER Forum and search "IBAM". It might be in the STICKY Thread called "COMMON Parts for FISHER's".

Measure the mA across the 10ohm resistor on each pin 5 (one probe on the tube side of the resistor, one probe to any chassis ground).
 
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