Matt's Sansui AU-317rebuild

Hi Matt,

If they don't look the same as the fuse resistors on the main amp board, and they measure OK then I would leave them as is. It may be the fuse resistors in this position changed during the production run, these were not identified in the service manual as being fuse resistors, but every 317 I have looked at had fuse resistors fitted to the tone control board.

Cheers

John

Thanks John

I'll leave them as is for now then!

-Matt

skippy124 said:

Hi Matt,

If they don't look the same as the fuse resistors on the main amp board, and they measure OK then I would leave them as is. It may be the fuse resistors in this position changed during the production run, these were not identified in the service manual as being fuse resistors, but every 317 I have looked at had fuse resistors fitted to the tone control board.

Cheers

John

Click to expand...

SUCCESS!

I got my last order of parts today and installed them in a few minutes. I fired it up slowly while monitoring the main power supply. The protection relay clicked in at about 60 V. I then dialed in the bias for each channel and the DC offset and now I'm listening to sweet music!

Everything seems to work perfectly, with one exception. I am getting some bleed through from the auxiliary input to the other inputs. It isn't super loud, but it isn't quiet either. Has anyone else experienced this?

The only parts I have not replaced yet are the zeners recommended by AUD101. I'll do those before buttoning it all back up.

-Matt

CONGRATS!
I pods have a tendancy to overdrive ( based on HP level set ) ....
Any unused inputs... get an RCA shorting plug....

Congrats!

Do you have new pictures of your unit?

Hi Karl,

I will post some pictures tomorrow!

I still have what I now believe is excessive bleed through from one source to the next. Even when an unused source is grounded and selected I still hear a significant amount of (distorted) sound from the live input. So I'm not out of the woods yet .. my first inclination is that I have a bad ground somewhere.

-Matt

I've done some additional testing on the signal bleeding, and here is what I've found:

1. With a source connected to the auxiliary input I have bleed through to the phono and tuner inputs

2. With a source connected to the tuner input I have bleed through to the phono input but not the auxiliary input

3. The bleed through is distorted (but not much) and unaffected by the master volume, balance, or tone controls

4. The issue is within the preamp section; removing the pre-out main-in jumpers there is no signal (this may be obvious, but I wanted to rule out some fault in the amp)

5. Both channels exhibit the same behavior

I just hit the input selector with another shot of D5 and am going to let that settle for a before doing more testing. Unfortunately I do not yet have a scope which would be very handy for this particular issue.

Looking at the schematic I'm having a hard time figuring out how signal could be leaking from one input to another and *not* be impacted by the balance or tone controls.

-Matt

More testing .. I now get severe crackling and popping when I fire it up! Seems that cleaning the selector switch aggravated something else. The problem is in the preamp since the crackling goes away when I remove the rear panel jumpers.

I've read that it may be the differential pair. If so, I believe that would be TR03-TR06 (2SA906) on the F-2752 control amp board which can be replaced with KSA992, which I happen to have on hand.

Does this make sense?

Thanks again guys!

-Matt

UPDATE: It wasn't the 2SA906s. I just swapped those out the problem persists. I'll have to see if I can borrow a scope from someone at work - that would make this much easier.

Hi Matt,

I have and several Sansui amps with flakey 2SA906 Transistors (317 and 717). Snaps, crackles and pops. The KSA992 is a good replacement.

And good work so far!!

Cheers

John

Thanks John!

The KSA992s didn't help - I'm still getting loud crackling and popping. It is loud enough that it trips the protection circuitry and makes terrible sounds through the speakers. So something clearly isn't right now, which is very unfortunate since it was basically working. I did not replace the 2SA906s in the phono stage, but those shouldn't matter since I'm experiencing this with the aux and tuner inputs.

John, in your experience were the bad 2SA906s causing loud crackling and popping similar to what I'm experiencing, or just more background noise?

I've looked around for any cold solder joints and haven't found any. I've also inspected everything and I see no obvious issues. The amp section is fine, so the problem is clearly in the preamp somewhere. It seem like a bad ground, but everything looks good visually.

Do you think it's also worth replacing the 2SA872s and 2SC1775s on the control amp board?

I suppose I also need to inspect the mic amp board more closely - the schematic indicates that the output of the mic amp board connects directly the pre-out, bypassing F-2752 altogether. This would mean that any noise induced by the mic board would not be impacted by the tone, volume, or balance controls.

-Matt

Hi Matt,

The 902's will definitely cause popping and crackles that will cause the protection circuit to engage, I have just had that issue with a 517.

I have also had problems with the 2SA872 and the 2SC1775 that will cause the same pops and crackles, you can use the KSA992 and KSC1845 to replace these.

These can decide to go noisy at any time, and it may be that just some nearby heat from th cap replacement has tipped one of the " over the edge"

Cheers

John

Edit - forgot to answer your question re the mic board. The output of this board is shorted via the mic jack unless a microphone is inserted.

Thanks again John!

I believe I have some KSC1845s so I'll try swapping both the 2SA872s and 2SC1775s tonight.

I did not see that the input to the mic board is shorted by default - thanks for pointing that out.

-Matt

Matt, Sorry to hear you have prob's with the pre-amp section of the AU-317 after your refurb - I already see skippy124 has given you some good advice - :thmbsp:

Although severe crackling and popping could point to transistor prob - Just for good measure - Carefully check the black ribbon cable that links the Phono EQ/Input selector switch to the Tone board for any breakages (continuity check), also check that the pcb pads it is soldered to are sound as they can lift and detach from the pcb track.

Thanks AUD101. I've double checked the ribbon cable and verified continuity on all of the pins. All of the solder joints and pads look good too.

So I proceeded with replacement of the 2SA872 and 2SC1775 transistors. There are only two of each on the F2751 board, but unfortunately I must have done something wrong since I let the smoke out of something when I powered it up. It was those last four transistors that caused the smoke - I'll double check things and pull each transistor one at a time and give them a sniff. Hopefully I just put one in backwards and didn't do much damage to the other components.

I noticed that there are also two 2SA917 transistors on this board as well - should I replace these too?

-Matt

Well, it looks like I made a boneheaded mistake. After replacing seven of what I thought were eight total transistors on the 2751 board, I pulled the eighth without checking what it was and just stuck in the last 2SA992 I had set aside for this board in its place. It turns out that it should have had a KSC1845 .. oops! That was TR08, so I'll swap that one out and then get the last two transistors that I didn't see at first. I'm hoping that I only lost TR08 and nothing else.

Normally I check everything I pull out before popping in a replacement .. I got a little sloppy this time and it burned me!

-Matt

Final update for the night. I was working on the wrong board the whole time .. I replaced all of the transistors on the 2751 board which is the head amp! No wonder the transistor subs I made had no impact on the crackle and pop!

I just swapped out the transistors on the control amp board (2752) and now things are back to normal. It is dead silent and there is no crackle or pop. Thanks guys!

-Matt

Great to hear that the crackles and pops are gone. And you won't have any problems with noise from the head amp/equaliser board seeing that those transistors have been replaced too!

Cheers
John

+1...Great to hear your AU-317 is back in service - Don't forget to post some pix soon - as it will help out future restorers

Yes - pictures will be posted soon!

I need to double check the DC offset and bias now that I've swapped out all of the transistors in the preamp section. Once I do that I'll button it up and take some pictures! I will try to do this by the end of the week.

-Matt

AUD101 said:

+1...Great to hear your AU-317 is back in service - Don't forget to post some pix soon - as it will help out future restorers

Click to expand...

Hi,

Changing the pre-amp transistors won't affect the bias and offset as the pre-amp output is capacitor coupled.

Look forward to seeing some pics

Cheers

John