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SA-9500 rebuild complete but fuse blew when testing, please help!

S

Segasonic91

Active Member
I started on my Jp AU-9800 tonight. I changed the 1451's on the switch board because I am still waiting for film caps from mouser and I wanted to do it all at once. I decided to change the 1451's because I want to use it now. I will eave the rest for when I have ALL the components.

I had....a LOT of trouble with the 1451's! One foil lifted but stayed intact. By the end of it, 4 or 5 foils were lifted, grrrrrr! I want to punch whomever designed that board with three 1451's UNDER the goddamned switch bar! It was a terrible struggle to get them in! THEN I noticed after finally getting the rotten things in place, I realised that I put them all in the wrong way! So then I had to take the out and start again!

Once I was finished, I checked continuity for all three legs on all of the 3503 transistors. They passed except for one, so I bridged it with a small wire and then it was fine.

Now the problem.... When I turned it on, I heard the relay click which was a relief. I plugged in one of my TTs and tested it. It worked, but I was missing a channel and I am not sure why. Was also the same with my CD player, so it is not just a phono problem. What should I check for a missing channel? I plan to check the voltages tomorrow. Any help is greatly appreciated!
 
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No, I noticed it when I put my last transistor in, so there was no power with the transistors in the wrong way.

My mind was not working due to stuff going on, I guess. I kept a 3503 in the transistor tester so I could keep checking the leg positions! Yet I STILL did it incorrectly! I was installing them as if the 2nd leg was base, but base was 3rd. Grrrr.
 
Well that’s good news. You caught the issue and corrected it before damage was done.

I’d personally start by looking for broken traces or bad solder joints in the area you worked on. There’s a chance that with the foil lifted that one or more isn’t making a solid connection.
 
I may have an idea of what the problem is.

I checked continuity again, and it is all fine. But the is a spot next to the middle "under the bar" transistors is a empty solder point. There is solder there, but nothing in the hole. Looking at the service manual, there should be a ceramic cap there. I can see the leg in the other side so the other leg must have come out when I was de-soldering.

I am not taking it apart again at the moment. I looked at the mouser order again and if I cancel two items, the order will ship right away. Turns out that I had doubled up on one of the film caps and THAT was holding up my order. The other back ordered item is just two transistors that I can probably do without. So I will hopefully have the order next week, and then I can do the whole thing at once and check that ceramic cap, too. I just hope to christ the cap is not under the transistor. I do not want to take those things out again! I lost 5 transistors trying to get them in those 3 spots. If anyone has a tip for an easy way to do it, please let me know! I cut the legs to try and make it easier to get the giant friggin head under the bar, but it did not make it easier.
 
YES, pictures!! That board does have some "via" holes that DON'T have components in them!!!

In a modern plated thru hole board, it would be shifting the signal from one side of the board to the other,

These EARLIER boards either were made without plate-throughs OR the plate-throughs have failed.

This is one board that I THOROUGHLY go through and solder in component leads in EACH AND EVERY hole, making SURE both sides are GOOD, CONDUCTING solder joints.

There also are MANY component leads that are used as via's and must be soldered on both sides.

I STRONGLY suspect that this is your current problem. That willy-nilly desoldering has left you with some disconnected circuits.
 
Hi Mark

Haha, there was no "willy-nilly" desoldering, I assure you. I followed the diagram in the SM and desoldered only the 1451's. When I saw that empty hole, I was confused. I did fill it with solder though.

I will get some pictures once I have the amp apart again to do the caps.

I should have just installed those three difficult transitors on the bottom of the board. Would have saved that damage!
 
I know you want a sure fire solution.
In reality it’s a culmination of experience in fixing ones mishaps.
In most cases, it’s requires a good visual inspection, performed when you have a good rest and mind set.
Magnifying glass and proper lighting will help immensely.
The circuit works in a symbiotic way, so sometimes it’s difficult to pinpoint by voltage checks. Plus the malfunction is not part of a logical failure.
Keep working it, you’ll find it. This is a good learning experience.
 
FINALLY got my mouser order today. Man ot yakes them forever to actually ship an order. Is this normal due to volume or the dreaded covid?

EDIT: Found (and recieved, thank you) my answer :D

Can finally get to work on this thing tomorrow. Have a mint UK 1E/1E Ziggy Stardust coming tomortow with some other Jp Bowie records and I am dying to listen to them.
 
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They’re usually pretty fast. COVID has slowed things - both their process due to warehouse safety protocols and receiving stock from manufacturers.

Film caps are bipolar.
 
nicholas2381 said:
They’re usually pretty fast. COVID has slowed things - both their process due to warehouse safety protocols and receiving stock from manufacturers.

Film caps are bipolar.
Click to expand...

Haha, thanks. Just as I found the answer and was about to edit so I do not look like such a moron, I got the alert that a message was posted. Have not used films before and I had not taken out the few sub-1uf caps in the SA-7500 nor recapped the tone boards etc on the SA-9900. Was unsure if those small caps were bi or not.
 
Doesn’t make you look like a moron at all. Good to ask if you don’t know. I soak up as much info here as I can. I’m still a novice at this so I have much soaking left to do.:rolleyes:
 
Don't beat yourself up over it. We've all BTDT at one time or another, and another, and another....... But just in case....

ANSWER FEES!
Answers..............................................$1.00
Answers which require thought..........$2.00
CORRECT Answers..........................$4.00
Dumb looks, Face Palms, and General Laughter from the Peanut Gallery in the Forum at that Mastercard "Priceless" Moment.........STILL FREE! :rolleyes::rolleyes::rolleyes::D:D:D:D:D
 
Are fast blow or slow blow fuses recommend for amps? I replaced a blown fuse in my AU-9900 and the guy at the shop said to use slow blow. I was testing it later that night, plugged in a TEAC 3340S R2R and after a few minutes the amp made a horrible noise and went into protection. I turned it on again and the same thing happened, but it is now stuck in protection, AGAIN! Would a fast blow have reacted faster and saved whatever the hell is blown this time?

I figured I may as well change the fuses in the SA-9800 while I am in it. I will hopefully get a start on it tomorrow. It is difficult becasue I don't have a desk at the moment to work at.
 
I was bagging up the caps tonight so I can start the job tomorrow.

Turns out I only ordered 10 4.7uf MKS2 caps and I need 15. I will have to use regular caps to fill the gap. Is it best to put the film caps on the control board or the tone control board?

Also, I realise why I had such a tough time with the 1451's on the control board. They are in a straight line underneath the bars on the SA-9800 where as it looks like the top and bottom of those three are off to the right of the bars. Looks MUCH easier! No wonder I had such a hard time with them and did not see it mentioned in other threads!
 
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