What would be the best replacement here?
KSA1220AYS is discontinued.
Would a TTA004B,Q be appropriate (I could borrow one from my A1 as there are long lead times..)
Or is there a better solution? And given the confirmation of your predicted short, would you first like to see some other tests/replacements?
KSA1220AYS is discontinued.
Would a TTA004B,Q be appropriate (I could borrow one from my A1 as there are long lead times..)
Or is there a better solution? And given the confirmation of your predicted short, would you first like to see some other tests/replacements?
2SA777(ecb) is listed as a low (audio) frequency driver for a 25-30W amp, Pc=750mW
2SA941(ecb) as a low noise audio amplifier, Pc=100mW
So KSA992(ecb) appears to be a reasonable fit, Pc=500mW, Ic=50mA matches 2SA941.
KSA1220(ecb) and TTA004B are overkill but I like the sentiment, KSA992 while it meets the needs
might be prone to stress/failure.
Suggest go with the KSA992 rather than harvest parts from the A-1. Possibly some other
alternatives, KSA916, KSA1013,,,
2SA941(ecb) as a low noise audio amplifier, Pc=100mW
So KSA992(ecb) appears to be a reasonable fit, Pc=500mW, Ic=50mA matches 2SA941.
KSA1220(ecb) and TTA004B are overkill but I like the sentiment, KSA992 while it meets the needs
might be prone to stress/failure.
Suggest go with the KSA992 rather than harvest parts from the A-1. Possibly some other
alternatives, KSA916, KSA1013,,,
Thanks MBZ.
Deducing the location of that faulty transistor is something I really wish I could do.
So, just swap one of these in and see how the amp sounds?
Does anything else need to be looked at, or swapped before firing up again?
Not looking to do extra work, I’ve spent more than enough time on this amp..
Deducing the location of that faulty transistor is something I really wish I could do.
So, just swap one of these in and see how the amp sounds?
Does anything else need to be looked at, or swapped before firing up again?
Not looking to do extra work, I’ve spent more than enough time on this amp..
-46V on the -30V pin is a bit of a give away that the regulation is not working. You just needed to slow down a little and think about it. Yeah, swap out the failed transistor, it might blow again, seems there is some history of problems with the 30V supply. Diode test TR626, would like to see a c-e short there since it's the main current supply path. Check solder joint on TR626,7 these are heatsink mounted, joints may deteriorate under the heat cycles.
Opening a sparkling wine this evening!
Thanks MBZ, as BB King nearly sang, 'The Hum is Gone.'
Thank you so much!
I pulled a recently installed TTA004B from my A-1, and dropped it into TR628 and it fired up 'perfectly.'
Fine to leave it there for now and only change if there's an issue?
Amp seems to be working very well across the board, all switches work without crackle, and everything as it should.
One thing, a fair bit of audio bleed through from Aux to Tuner. But not from Aux to Phono.
Any suggestions?
I planned to recap the Function Board with Muse and some film caps. Might this help?
Would you recommend getting this recap done (all the other sections of the amp have already been recapped) before installing it in the main system, or just get to know the sound of those old original Silmics?
Any other checks and readings I should undertake on this Flat Amp Board, especially in the area of this replaced transistor?
Thanks MBZ, as BB King nearly sang, 'The Hum is Gone.'
Thank you so much!
I pulled a recently installed TTA004B from my A-1, and dropped it into TR628 and it fired up 'perfectly.'
Fine to leave it there for now and only change if there's an issue?
Amp seems to be working very well across the board, all switches work without crackle, and everything as it should.
One thing, a fair bit of audio bleed through from Aux to Tuner. But not from Aux to Phono.
Any suggestions?
I planned to recap the Function Board with Muse and some film caps. Might this help?
Would you recommend getting this recap done (all the other sections of the amp have already been recapped) before installing it in the main system, or just get to know the sound of those old original Silmics?
Any other checks and readings I should undertake on this Flat Amp Board, especially in the area of this replaced transistor?
Double check the +/-30V supplies.
Switches are problematic in vintage, you could try gently rocking each switch
in turn and note any affect (good or bad) on the bleed. For the push button
switches apply light pressure without switching. Then for all switches, fully
switch a few times again note any effect. Switch may need deep cleaning, ie,
disassembly then clean.
Switches are problematic in vintage, you could try gently rocking each switch
in turn and note any affect (good or bad) on the bleed. For the push button
switches apply light pressure without switching. Then for all switches, fully
switch a few times again note any effect. Switch may need deep cleaning, ie,
disassembly then clean.
DC voltage readings attached in screenshot.
AC readings from the same location (+ / - 30) read 0.00
Also, adjusting DC Offset as per the SM, am able to get readings of:
0 mV, +/-40mV (readings rise and fall within this range.)
Are these readings ok, or do some diodes (I have stock,) or anything else need swapping?
AC readings from the same location (+ / - 30) read 0.00
Also, adjusting DC Offset as per the SM, am able to get readings of:
0 mV, +/-40mV (readings rise and fall within this range.)
Are these readings ok, or do some diodes (I have stock,) or anything else need swapping?
Voltages look good, read elsewhere that the EQ dc offset voltage does bounce about, spec is 0 +/-200mV so +/-40mV is great.
That’s great news, thanks for letting me know. So, no need to go swapping diodes then?
Before tracking down the hum issue became such a mammoth time consuming task, I’d intended to put my efforts into recapping the the Function board with Nichicon Muse, especially the bipolars, and the lower value caps with films.
This board is actually full of Elna caps (originals?) and any that I’ve pulled and tested have been ‘good.’ Before buttoning up would you leave as is, or repopulate with new caps? Realise that this can be a touchy subject so feel to DM so that thread doesn’t lose its core message and fantastic result.
Before tracking down the hum issue became such a mammoth time consuming task, I’d intended to put my efforts into recapping the the Function board with Nichicon Muse, especially the bipolars, and the lower value caps with films.
This board is actually full of Elna caps (originals?) and any that I’ve pulled and tested have been ‘good.’ Before buttoning up would you leave as is, or repopulate with new caps? Realise that this can be a touchy subject so feel to DM so that thread doesn’t lose its core message and fantastic result.
I'd leave the diodes alone, would expect noise/symptoms if they were misbehaving.
RE the recap, give it a good listen and go from there. I recap'd mine but I was after that last 1%. The function board is mostly for the phono stage so depending on your needs... I don't recall if the amp used those Duorex II caps, probably in later amps like my CX-1. Read a few posts that they didn't age well.
RE the recap, give it a good listen and go from there. I recap'd mine but I was after that last 1%. The function board is mostly for the phono stage so depending on your needs... I don't recall if the amp used those Duorex II caps, probably in later amps like my CX-1. Read a few posts that they didn't age well.
Hello All,
I am new on the forum and found this topic thanks to google.
I got one of these Yamaha C4 preamp and had a similar problem with it : no sound out.
I plugged in a smarthone as source and used an application to generate a wave signal to degug the C4, I found that all is OK except the subsystem in charge of the relay RY301, in fact the RY301 doesn't switch on.
I tried to check and degug this part with a little oscilloscope I had.
My conclusion is that the relay is OK. I focus on transistor TR621, the last component before the relay and I get -12V on the base and the collector, nothing on the emitter, that seems to be, at least for me, the command to switch the relay on.
As my knowledge in eletronics is not that much, and the print quality of my service manual is bad, I am wondering what can be wrong in this part (if the problem is really in this part). Something strange to me: the transistor used for TR621 is a ASD476A that is a NPN transistor supposed to be driven by a positive tension on base, so how can that work with a tension of -12V?
Can someone help me on this ?
Thanks in advence.
Didier
I am new on the forum and found this topic thanks to google.
I got one of these Yamaha C4 preamp and had a similar problem with it : no sound out.
I plugged in a smarthone as source and used an application to generate a wave signal to degug the C4, I found that all is OK except the subsystem in charge of the relay RY301, in fact the RY301 doesn't switch on.
I tried to check and degug this part with a little oscilloscope I had.
My conclusion is that the relay is OK. I focus on transistor TR621, the last component before the relay and I get -12V on the base and the collector, nothing on the emitter, that seems to be, at least for me, the command to switch the relay on.
As my knowledge in eletronics is not that much, and the print quality of my service manual is bad, I am wondering what can be wrong in this part (if the problem is really in this part). Something strange to me: the transistor used for TR621 is a ASD476A that is a NPN transistor supposed to be driven by a positive tension on base, so how can that work with a tension of -12V?
Can someone help me on this ?
Thanks in advence.
Didier
1. "Nothing" is not a valid multimeter reading.
2. I would suggest you recheck your TR621 pinout, as the combination stated makes no sense.
Here's the section in question:
If I had to place my bets, a leaky C313 (33µ/16V) would be my #1 candidate. That would prevent TR622 from turning on, thus keeping TR621 from conducting. Absolute classic fault.
I won't be surprised if the spot will fit a modern 35 V or even 50 V part, and would suggest using one.
Hello sgrossklass.
Sorry for the "invalid multimeter reading", it is my binary view of what should be this kind of circuit (I am computer programer ...) : either I have a tension (-11.1V as mentionned on the schema) and the relay passes to ON or I have null tension (0V, if I remember well, this is the value I measured) and the relay remains OFF.
I will check/replace C313 and see what happens then.
Thanks for this track.
Didier