Yamaha A-1020 Needs TLC

Karl vd Berg said:

Hi James,

One question, did you replace the Toshiba's 2SA1145-O with same PNP or another Toshiba sub? I'm just curious because I have a bunch of these and believed they are pretty good trannies.
If you replaced them, which other ones did you use?

Nice to know everything went well. I too have to modify the PCB quite a few times to place new components, like new trim pots.

The total of €54 in cost was not that bad considering a mighty A-1020 is running again. :yes:
No idea the retail price of the amp back in 1985, but being TOTL might cost a lot then.

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Now, are you ready for another vintage amp?? :thmbsp:

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Mouser still has original Toshiba 2SA1145-O's in stock, listed as an "End Of Life" product. They showed something like 1900 of them still in stock. So I bought 25 of them. Heads up to anyone wanting to stock up on them, get 'em while they're hot!

I figure the total cost as quite low considering that the amp is in many ways like new inside, and the outputs & drivers have a higher load carrying ability than original.

I cut 2 legs off of one of the old dead outputs as donor legs for the middle trim pot leg. Bent 90° and soldered in before the trimmer and sat the trimmer on top of it. Sorry, didn't have my camera with yesterday.

Beautiful amp. Your's? Looks like new.

Cheers,
James

Edit: Avionic linked to these Bourns trim pots in Acetate's "Fixing a Yamaha M-65 For a Friend" thread (thanks Avionic!)...

http://www.mouser.de/Search/Product...virtualkey65210000virtualkey652-3386G-1-102LF

The lead spacing looks a lot better than the Vishay trimmers that I bought.

Those CA-2010 are gorgeous.
Ditto the CA-1000

Bratwurst7s said:

Beautiful amp. Your's? Looks like new.

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No, just an internet pic. That is a legend from the 70s...

http://www.thevintageknob.org/yamaha-CA-2010.html

BTW, the owner of the A-1020 told me yesterday that the other Yamaha that he has that he is going to give me isn't an AX-800 (yes, I know that that number doesn't exist, I assumed that it would be an 850,870 or 890), rather it's an AX-700. So you can expect to see it show up in my AX-700 thread later.

And since it doesn't have a remote the guy that I was going to give it to after doing a referb doesn't want it. So I will have to find a new victim.

Cheers,
James

So it's been 2.5 months since I delivered the amp and last Friday I bumped into the owner and asked him how it was working. He answered that he still hasn't hooked it up yet. It's sitting in a closet. I'm crying. :tears:

Recently I read in a thread where Avionic recommended replacing the diodes in a channel that had suffered blown outputs+ because they had probably been stressed hard. Which made me think about the fact that I had only pulled, measured and then reinstalled the diodes in the A-1020, but replaced almost all of the transistors.

I have a bunch of 1N4148 and 1N4007 diodes on hand, and if I'm reading the data sheets correctly wouldn't they be good replacements for most of the diodes in the A-1020 (excepting the zeners)? And would it be worthwhile or recommended to replace the old diodes if the amps owner would want to bring it back to me?

Cheers,
James

... bringing the thread back to life ..

my English isn't the best (lack of practice) but i hope it's good enough

Hello Forum,
I was searching for an new (old) amplifier with more than 100W rms to power my IMF Professional Monitor transmission line speakers I introduced in this thread.
I used to have an Marantz PM-64 mkII until it died a few years ago. I wouldn't give it away these days, but back then, I was not able to fix it.

Price for good old HiFi is very high nowadays but I found an Yamaha A-1020 with some issues for a small double-digit amount. The previous owner told me that after approximately 20 minutes the sound falls silent. I powered it on for a test and it was as he described.

By searching the net I came up to this thread and got in touch with James (Bratwurst7s). James is very helpful and with his support I try to get the A-1020 repaired.
First step is to fix the main problem. Once that's done, I think about a general overhaul.

With the permission of James I will show the progress here maybe it will help somebody else who is in an similar situation. ... you are welcome to submit your suggestions or ideas here

some traces of use and the front cover is missing





regards
Andreas

after some rough cleaning
the ugly glue did his job ..



James helped me to find the proper spare parts that I ordered today
I hope the main problem is fixed by replacing the bad parts and some capacitors





until the order arrives I spend some time with cleaning the switches, volume control, input selector, ..... and making an dim-bulb tester

Hi Andreas!

The left jumper wire in this photo looks completely corroded in the middle. It, the one on the right and any others that are corroded need to be replaced. You can use the trimmed off leg of a resistor or capacitor for wire. It just needs to be 0.8mm and tinned.



Cheers,
James

... delivery of my order should be today

@Bratwurst7s
Thank's James, i will check very carefully which parts are corroded.
At the moment i could only see defective parts at the glued areas

for dummies ....

While you're in there inspect the solder joints on the driver boards mounted to the heat sink. On mine I noticed that the solder joints were cracked to the point the transistors were loose in the board.
Mine worked fine even with glue corrosion and the loose transistors which I thought was pretty amazing.

OMGCat! said:

While you're in there inspect the solder joints on the driver boards mounted to the heat sink. On mine I noticed that the solder joints were cracked to the point the transistors were loose in the board.
Mine worked fine even with glue corrosion and the loose transistors which I thought was pretty amazing.

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That's a very good point. IIRC those boards have the TO220 driver transistors and a little 2SC2240 that (?) does thermal tracking.

Andreas: I would resolder every connection on those 2 boards. I don't like the way that the right one is bent out of position, look that one over very closely. Also, you will need some thermal paste when re-mounting them to the heat sink. Do not use any thermal past meant to be used with PC's that has silver or any other metal in it. Just plain old white thermal paste or sil-pads.

OMGCat: Just so you are up to speed, Andreas contacted me and said that the amp quit after 20 minutes of use, both channels. After seeing his photos and seeing that the bad (leg eaten off) 680pF cap C339 is in the protection section I told him to replace it and all other corroded parts and then either start a new thread or post here.

I don't have experience with an amp quitting like this. Usually they just make smoke and sometimes loud noises. So other than the glue corrosion it looks like protection or PSU? Andreas has built a dim bulb tester. I regret now not telling Andreas to replace all of the Elcos in the protection section but I wanted to see what replacing the corroded parts did before going further. Any thoughts that you have are welcome.

Cheers,
James

Bratwurst7s said:

That's a very good point. IIRC those boards have the TO220 driver transistors and a little 2SC2240 that (?) does thermal tracking.

Andreas: I would resolder every connection on those 2 boards. I don't like the way that the right one is bent out of position, look that one over very closely. Also, you will need some thermal paste when re-mounting them to the heat sink. Do not use any thermal past meant to be used with PC's that has silver or any other metal in it. Just plain old white thermal paste or sil-pads.

OMGCat: Just so you are up to speed, Andreas contacted me and said that the amp quit after 20 minutes of use, both channels. After seeing his photos and seeing that the bad (leg eaten off) 680pF cap C339 is in the protection section I told him to replace it and all other corroded parts and then either start a new thread or post here.

I don't have experience with an amp quitting like this. Usually they just make smoke and sometimes loud noises. So other than the glue corrosion it looks like protection or PSU? Andreas has built a dim bulb tester. I regret now not telling Andreas to replace all of the Elcos in the protection section but I wanted to see what replacing the corroded parts did before going further. Any thoughts that you have are welcome.

Cheers,
James

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I think replacing the damaged parts is a great start and needs to get done before any further troubleshooting is done. The driver boards and any other cracked solder joints would be my next target. The last A-700 I repaired had issues where it would go into and out of protection and the bias was all over the place. The cause was cracked joints all over and repairing them got the amp to run properly.
I'm curious if after 20 minutes it quits altogether or if the protection relay opens. Either way, there is plenty of low hanging fruit with the corrosion and cracked joints. The fact that it works properly some of the time to me means that there is probably nothing badly wrong in there.
Mine was well used and none of the capacitors had dropped in value to the point of causing a failure so I don't think you've lead him astray by not recommending them all to be replaced just yet.

Thank you all for your suggestions and taking part to help me.
After comparing some photos of the inner life of the A-1020, I think that someone before was already on the device.
Maybe one of you got a picture of an untouched one, I couldn't find one.

Question: Has the thermal connection from the transistors to the heat sink to be electrically isolating?

I have some white thermal paste and heat conductive double-sided adhesive tape (mounting of heat sinks on cruise control units of rc cars),
I think the adhesive tape is not not suitable for high temperatures, so I will use the thermal paste.
I will resolder every connection on those 2 boards and other connections that don't look good.

The workbench is prepared, this evening I start soldering !

If the amplifier works properly after replacing the apparently defective parts, I will think about further steps.
I would like to test it for a while ( .. listening to good music ..), then I can imagine a general overhaul and replace wearing parts.

I can't tell from your photo but if the original 2SA1265N (green) and 2SC3182N (black) plastic case output transistors and the smaller TO220 plastic case transistors are on the daughter boards (I can't remember their numbers at the moment) are still in the amp then you don't need electrical insulation.

Good luck, take your time, and let us know how things progress.

Please take a few photos of the areas that make you think that someone has been in the amp. Also take a few photos of the daughter boards before you remove them from the heatsink.

Cheers,
James

edit: Daughter card transistors: 2SA1306A & 2SC3298A (TO220), 2SA970 & 2SC2240.

here are some pictures ...



on foreign images I saw some different components, but I don't know if they were already replaced there
But that's not the point now, just for interest it would be nice to have a photo of the inside of an untouched original.

Yes, I take time and will keep you up to date.

Those sloppy looking solder connections on the main output transistors are actually original going by my experience so far. And the transistors on the small boards are original, the fusible resistors also look original. You are good to go with them after re-soldering.

Cheers,
James

Soldering is done.
The small boards definitely needed an overhaul.
I found a box of metal film resistors that I bought some time ago, so I replaced some more parts than planned.

I didn't really want to invest that much work in the moment, but since the amp was already dismantled I started with a more accurate cleaning.
The parts that fit into the ultrasonic cleaner were cleaned and then blown off with compressed air.
The other parts I treated with a soft brush and cleaning liquid, now everything will be dried for a while.

so far for now ..

Hello again,

Work goes ahead, some questions

is there a simple explanation why these cables are not directly soldered?


@Bratwurst7s
James, did you find a replacement for the big 22000 µF capacitors back then?
( not that I want to replace them, just out of interest )

Hi Andreas,

Nice work!

The owner of the 1020 that I worked on took it down to Italy and wasn't interested in replacing those big filter caps so I never pursued it farther. Sorry.

The wire connections that are in your photo are called "wire wrap" and are actually an excellent connection. They hold up well to vibration and temperature changes. Where the wire contacts the post there is an oxygen-free "cold weld". As long as they are never unwrapped or badly disturbed the connections can actually hold longer than a solder connection.

If you ever need to remove the board it's best to de-solder the post blocks from the board and leave the wire wrap undisturbed.

Cheers,
James