SX-1980 Recap Assistance
- Thread starter bbauer01
- Start date
the architect
AK Member
yeah, that's just wow. WTF?! :sigh:
bbauer01
Active Member
This is definitely not original. If I am following this correctly, it looks like the current source circuit has been re-created. The q207 fet, c229 capacitor, and the d210, d211 zener diodes have been eliminated. The trace between the drain leg of the fet and the base leg of transistor q209 has been cut. A 82k ohm resistor has been added that appears to bridge the base side and collector side of q209.
Sorry for the rather primitive drawing, but it was a quick and easy way to show what is going on. It was faster for me to print out and enlarged section of the service manual, and then use whiteout and a pencil to show modifications.
This isn't all of it either, this only shows the modifications to one current source circuit. On the other circuit, there is a cut trace and a resistor on the backside of the board. I haven't mapped this out yet.
The big question now is what do I do with it? Do I leave it alone, since it works... or is it a ticking timebomb that should be dealt with while I have everything apart?
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anderslober
Yikes...not again!
Great thread.....keep the info and pictures comin'. I hope you get it running again.
Very nice.
Very nice.
I was under the impression it's running now - just that he wants to make it right for the long term.
bbauer01
Active Member
Oh, it runs... It is now just a matter of making it right. This sx-1980 was apart for a recap. Sometimes I wish I never opened 'er up... as they say "ignorance is bliss" If I put the lid back on it this way, I think that I would cringe every time I flipped the power switch.
At this point, I just need input on what to do with the power supply board.
EDIT... nevermind, I know what needs to be done. The current source circuits need to be rebuilt, as well as new caps and new TO-220s, TO-92s
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bbauer01
Active Member
I ordered the first round of parts.
I chose: (caps list is earlier in this thread)
Nichicon KL Caps for the Low Leakage, and tantalum over 1uf (ceanl / czsa)
Nichicon PW Caps for the rest (cea)
polyfilm caps to replace tantalums 1uf and less
ZTX795A / ZTX694B to replace the TO-92s on the power supply
MJE15032 / MJE15033 to replce the TO-220s on the power supply
17v/18v 500mw zener diodes
I also PM'd Echowars about his current source, since I will need to do something about that. In its current state, there is a resistor in place as a current source (replacing the fet and diode circuit) on the -80v supply, and the +80v supply has a resistor between the base of q208 and the gate of the q206 fet.
I chose: (caps list is earlier in this thread)
Nichicon KL Caps for the Low Leakage, and tantalum over 1uf (ceanl / czsa)
Nichicon PW Caps for the rest (cea)
polyfilm caps to replace tantalums 1uf and less
ZTX795A / ZTX694B to replace the TO-92s on the power supply
MJE15032 / MJE15033 to replce the TO-220s on the power supply
17v/18v 500mw zener diodes
I also PM'd Echowars about his current source, since I will need to do something about that. In its current state, there is a resistor in place as a current source (replacing the fet and diode circuit) on the -80v supply, and the +80v supply has a resistor between the base of q208 and the gate of the q206 fet.
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This might give you a start...
(PM me)
Morning cup of coffee?
That much caffeine would kill a horse.
The rest of it.... a VERY familiar view.
Whatcha gonna do about the EchoWars current source?
Yes, that is a MTF rebuilt Power Supply, with MTF builds of EchoWars's current sources, operating...
and follow these links:
http://www.diyaudio.com/forums/solid-state/92904-pioneer-sx-1980-regulator-driving-me-insane.html
here's the document:
http://www.audiokarma.org/forums/attachment.php?attachmentid=50480&d=1180659339
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Sorry..has been a very busy day. I'll get back to you late tonight or sometime in the morning.
I'm curious as to what the ramifications of this is. My PS PCB has the same configuration in two locations related to the eighty volt power supply.
bbauer01
Active Member
I made a mistake when typing. I meant to say...
the trace between the gate of the q206 fet and the base of the q208 transistor has been cut and the 470ohm resistor placed between them. I edited the earlier post.
bbauer01
Active Member
MTF... thank you for the info. I saw that thread, read it, but somehow missed the word document.
I noticed on the picture of your current source that you used TO-126 cased devices to replace q213, q212. My plan was to replace all of the TO-92s with ZTX795A / ZTX694B. Is there a better choice for q213,q212?
Also, should I move the TO-220s back onto the board when I replace them with the MJE15032 / MJE15033, or leave them mounted to the output heatsinks?
The to-126 cases are optional - stick with the zetexes... they really don't get hot and the zetexes can handle some momentary current and heat when necessary.
I've been using Fairchilds, and thus a few to-126's...
hard to say about moving the to-220's.... I've been concerned about their heat load from the start, but the idea of pumping more heat into the power amp's heat sinks than it is generating itself just seems like asking for obscure problems.
I've been using Fairchilds, and thus a few to-126's...
hard to say about moving the to-220's.... I've been concerned about their heat load from the start, but the idea of pumping more heat into the power amp's heat sinks than it is generating itself just seems like asking for obscure problems.
These TO-220's get hot enough to raise the temp of the heatsink, which will muck with the bias current. You may attempt to mount them remotely somewhere, but I'd not do it on the output transistor heatsink.
I have taken to replacing those 220µf 160V axial caps with short, fat radial caps (Panasonic ED, #P13512-ND)...intentionally mounting them 'off center' to keep them as far away from the heatsink as possible. This allows more airflow around the heatsink, and keeps the capacitor cooler as well. It is not the neatest solution mounting-wise, but if you replace those hot-running TO-220's with nice rugged On-Semi transistors (MJE15032/33), then I think it's a combination that ought to be good for 20 years or more.
I have taken to replacing those 220µf 160V axial caps with short, fat radial caps (Panasonic ED, #P13512-ND)...intentionally mounting them 'off center' to keep them as far away from the heatsink as possible. This allows more airflow around the heatsink, and keeps the capacitor cooler as well. It is not the neatest solution mounting-wise, but if you replace those hot-running TO-220's with nice rugged On-Semi transistors (MJE15032/33), then I think it's a combination that ought to be good for 20 years or more.
bbauer01
Active Member
Thank you. I will mount them all back on the board.
Also... The capacitor list in my previous post has been edited to include the 'mystery board' AWG-058 that is commonly missing from most online-available service manuals. The list should be complete now.
Pictures to come tonight. I should get a few boards done. I am avoiding the power supply board until EW's current source boards arrive, since my plan is to tackle the current source issue first and work from there.
bbauer01
Active Member
Well tonight I got the following done: AWF-030 EQ Amp, GWS-129 Function Switch Board, AWG-059 Tone Control Board, AWM-119 Filer Assembly, AWM-122 Power Amp Board. Here are a few before / after/ during pics. I replaced one capacitor at a time, then re-installed the board, dim-bulb tested, then powered on and verified... I guess I am a bit anal.
Tantalum caps on AWM-119 before.
AWM-119 after.
AWG-059 Tone Control after
AWF-030 EQ Amp ... just started
AWF-030 EQ Amp complete
Tantalum caps on AWM-119 before.
AWM-119 after.
AWG-059 Tone Control after
AWF-030 EQ Amp ... just started
AWF-030 EQ Amp complete
bbauer01
Active Member
This is the bottom of the tuner board AWE-093. Notice the capacitor and resistor on the foilside. Is this anything that I should be concerned about? I verified that all the components on the front seem to match the specs in the service manual. When I recap this board, I am planning on leaving these two components alone... any thoughts??
bbauer01
Active Member
As mentioned in an earlier post, I will be moving all of the TO-220 devices off of the output heatsinks, back to the power supply board. From looking at pics of other SX-1980s it looks like those devices had their own heatsinks. Is there anything comparable that I can get from Mouser to replace those? Or would it be sufficient to use the flat 3-sided aluminum heatsinks as the other 2 to-220s use. I have some parts units with that style heatsink... I am just not positive that will dissipate enough heat.
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I don't think the "U" shaped heatsinks have the capability - I'd use the larger style (in the picture of my recapped PSB below). I may have a few of that style I could give you though I'm not sure if I have the insulators for them. I'll check and send you a PM.
JimB
JimB