CA-800 issues - troubleshooting assistance thread

Uncle Bambi

Funky Tut
Ok - so, I was given a cosmetically near perfect CA-800, that the previous owner said died "after too many speakers were hooked up or something". I took it home, cracked the case, and found 2 blown 3A fuses on the left channel.

I replaced the fuses, hooked it up to a DBT and powered it on. At first, no reaction from the DBT, the power LED lit, and the relay clicked out of protection. I was fixing to hook up an Ipad on the AUX 1 input when DBT went bright and the relay clicked into protection. I had my hand on the switch so was able to shut it off right away.

Removing the left side fuses, I can power on and play with the right channel only. However, the music is distorted.

I'm going to presume that I have at least one output on the left side that is bad, and will pull and test them following Echowars helpful thread on the subject.

I've never worked on a Yamaha before, but this unit seems well laid out for maintenance and I was able to find the SM in the AK database so I think I've got a good handle on it so far.

As I've only done a few Pioneer units and a couple of Sansui's, I'm wondering if there are ant tips, tricks, or "well known" issues that would be helpful when working on a Yamaha (Sansui glue and fuse resistors, for example).

Also, I'm kind of curious as to why the right side is distorted.... could that be a function of the left side being off-line, or does that infer a problem on that side as well?

Any advice, guidance, or constructive criticism will be gratefully received.
 
Well - it seems right off the bat I need some assistance. :(

I downloaded the SM for the CA-800. It says the amp boards are NA06340, but mine are NA06627 ???????????

Transistors and pots are straightforward enough to figure out replacements for, but the zener values aren't listed in the SM. Does anyone have another SM or maybe experience rebuilding these amp boards? I could sure use a parts list if anyone has one put together, or maybe some insight on how to dig out the values from the SM - mine doesn't seem to list them.
 
No zeners on the amplifier sheets. D601-606 ----1N4148. D607 10D-1 1.5A 100volt
http://www.mouser.com/ProductDetail...GAEpiMZZMtbRapU8LlZD0HbIjlpuZ44W873Uj%2bOVqU=

Thanks for that sanity check. I thought I saw some bent ends on the board component silkscreens, but re-checking after your post reveals my error. I have all those on-hand, so that's not an issue.

The SM component layout diagrams are very fuzzy and hard to read - I sure wish they had a component list per board like the Pioneer and Sansui manuals. :)
 
I sure wish they had a component list per board like the Pioneer and Sansui manuals.

Me too..I should break down and buy a service manual for the 800 one of these years.:D
 
Hmmmm.......

I checked the left channel outputs, and one was shorted out. Replaced it, and still get a bright DBT. If I pull the fuses on the left, the right come on strong (after de-oxit :)). Also, the red power LED is dark when the unit is on.

What else could be drawing excessive current besides the outputs?

Also - I ran through the adjustments and they are all within spec. The only puzzler is the B class idling current adjustment. With the probes on TP3 and TP4, turning VR603 doesn't do anything..... for either side. Voltage reads "0" on the meter, but I must be doing something wrong....... suggestions/ideas?
 
Hmmmm.......

I checked the left channel outputs, and one was shorted out. Replaced it, and still get a bright DBT. If I pull the fuses on the left, the right come on strong (after de-oxit :)). Also, the red power LED is dark when the unit is on.

What else could be drawing excessive current besides the outputs?

Also - I ran through the adjustments and they are all within spec. The only puzzler is the B class idling current adjustment. With the probes on TP3 and TP4, turning VR603 doesn't do anything..... for either side. Voltage reads "0" on the meter, but I must be doing something wrong....... suggestions/ideas?

Check your left channel outputs again. May have blown another one on power up. also pull and check TR608 and 609 the driver transistors.
 
The only puzzler is the B class idling current adjustment. With the probes on TP3 and TP4, turning VR603 doesn't do anything

Either had a bad connection or the "Mode switch"(center switch between the two micro switches) is messed up(dirty). If "class A" adjusts and "class B" doesn't.
 
I'll check that. Class B didn't adjust, and I didn't try class A

If either fuse F601 or 602 were open or emitter resistors R630 and/or 631 were open you would read 0 volts across TP3 and TP4 .

When you replaced the output transistor , you did reinstall with the mica insulator between the transistor and heatsink ? Right :yes: And the replacement was the proper polarity (NPN or PNP ):yes: :D
 
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If either fuse F601 or 602 were open or emitter resistors R630 and/or 631 were open you would read 0 volts across TP3 and TP4 .

When you replaced the output transistor , you did reinstall with the mica insulator between the transistor and heatsink ? Right :yes: And the replacement was the proper polarity (NPN or PNP ):yes: :D

I'll resume troubleshooting tonight and report back. I did replace the mica, and I'm pretty sure I got the polarity right. I'll pull the outputs and double check, and then move on to the drivers TR608 and 609.

The fuses are intact, but I haven't ohm-ed out R630 and/or 631 yet. There was voltage on the left side - something like .012v, but 0 on the right.
 
OK - the original bad output is a PNP - 2SA663, shorted emitter to collector.

I replaced it with an Onsemi MJ21193G, which is a PNP

Now, I also tested the 2SC793 NPN and it tested good. Now that I've pulled it and re-tested, it is showing shorted emitter to collector.

GRRRRrrrrrrrrrrr.. :(

So - either the drivers or some other faulty part is causing this...... or could it be that pairing a new MJ21193G with the original 2SC793 caused an issue?

I'll pull the drivers TR608 and 609 and check them next.

ALSO - R630 and 631 are measuring about .5 in-circuit.
 
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Yeah - that's it. Typo. :eek: Edited post to reflect reality.



I pulled and re-tested the MJ21193G, and it shows good. Any idea what caused the 2SC793 to pop?

Possibly already weaken by the 2SA shorting out. They usually go out in pairs.
That explains a bright dim bulb...
 
Possibly already weaken by the 2SA shorting out. They usually go out in pairs.
That explains a bright dim bulb...

Good to know. I'm going to order 2 of each, and eventually replace both sides after I find the fault (which maybe I've done already.....:))

I'm still going to pull and test the drivers, but even if they are good I'm thinking of doing a full rebuild on both sides. So, I've been looking for acceptable transistor subs, and this is what I have so far:

2SA663 - MJ21193G
2SC793 - MJ21194G

SC1124 - KSC2690AYS
SA706 - KSA1220
SC734 - 2SC1815 or 2SC1845
SA561 - KSA1013

SA763 - ?????????? (help) :)

Does that list vet ok?
 
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