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Technics SA-828 Receiver from 70s- Is it worth trying to save this aging patient?
- Thread starter Iceman from McMurdo
- Start date
O.K.
Please add the IC601 DCV tests.
The list looks complete by now.
You should contact Digikey for checking/resolving the Trs suffix issue.
Then we shall approve the final list before purchase.
When the parts do arrive,
we shall re-construct(literally) the bad channel step by step from "left to right".
Measuring voltages between construction phases.
Please add the IC601 DCV tests.
The list looks complete by now.
You should contact Digikey for checking/resolving the Trs suffix issue.
Then we shall approve the final list before purchase.
When the parts do arrive,
we shall re-construct(literally) the bad channel step by step from "left to right".
Measuring voltages between construction phases.
Confirm . . . .
The original batwing power xstrs were bad in the left channel of the unit.
Did you lose yet ANOTHER set on your last test ?
If yes . . . .
Would you like me to give you a procedure, in order to not lose another set on the next power up ?
If so, include in your parts order, (2) 470 ohm 2 watt metal film resistors.
Also,do you have an analog voltmeter . . . .pointer type . . . to read 100VDC with?
The reason for your difficulty in the finding of those 20A99 diodes was the fact that they are germanium, have a higher than normal 100 VDC breakdown spec and a hefty 100 ma current spec vice most ordinary units 20 ma or so.
Regular SILICON diodes come out like cookies made with a cookie cutter-----photograph copies----Xerox copies---printed pages from a printer .
BUT such is not the case in the manufacture of germanium units, they also have back resistance to contend with.
Would advise replacing all 4 units . . .D617-619 and 615-621 with units of the same manufacturer . . . .which only seems to be available as the units now supplied by NTE . Don't know how long they will be able to keep stocking them.
73's de Edd
The original batwing power xstrs were bad in the left channel of the unit.
Did you lose yet ANOTHER set on your last test ?
If yes . . . .
Would you like me to give you a procedure, in order to not lose another set on the next power up ?
If so, include in your parts order, (2) 470 ohm 2 watt metal film resistors.
Also,do you have an analog voltmeter . . . .pointer type . . . to read 100VDC with?
The reason for your difficulty in the finding of those 20A99 diodes was the fact that they are germanium, have a higher than normal 100 VDC breakdown spec and a hefty 100 ma current spec vice most ordinary units 20 ma or so.
Regular SILICON diodes come out like cookies made with a cookie cutter-----photograph copies----Xerox copies---printed pages from a printer .
BUT such is not the case in the manufacture of germanium units, they also have back resistance to contend with.
Would advise replacing all 4 units . . .D617-619 and 615-621 with units of the same manufacturer . . . .which only seems to be available as the units now supplied by NTE . Don't know how long they will be able to keep stocking them.
73's de Edd
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Thanks Edd, yes, I did lose the replacement set of bat-wings - but think it was MY fault for taking the cheap way out and buying from the China-man (had a hard time finding anything else reasonably priced). I strongly suspect the replacements were fake or poor quality reproductions that failed on power-up, and then started a daisy chain of related component failures that took out most of the TRs on the left channel. Guess the other possibility is they simply failed due to other components downstream that we hadn't identified prior to power-up, but it makes no difference now - gotta be fixed anyway.
So, lesson learned... Don't take the cheap way out in the world of electronics! Have since found US vendor that can supply higher quality substitute bat-wings at reasonable cost, so plan to go with those. Plus, think we've pretty much gone thru everything else that might now be bad on that channel and will be replacing with new. And I agree with trying to source paired TRs from same manufacturer - just hard to find single source that can provide everything I need... At any rate, I have a substantial parts list tallied up and will be starting repairs soon!
Note to all - Must take a temporary break due to an upcoming trip out of town, but will be back online and providing further updates in a couple of weeks. Please stay tuned and continue helping me resurrect this beast! Appreciate everyone's patience. Thanks!
So, lesson learned... Don't take the cheap way out in the world of electronics! Have since found US vendor that can supply higher quality substitute bat-wings at reasonable cost, so plan to go with those. Plus, think we've pretty much gone thru everything else that might now be bad on that channel and will be replacing with new. And I agree with trying to source paired TRs from same manufacturer - just hard to find single source that can provide everything I need... At any rate, I have a substantial parts list tallied up and will be starting repairs soon!
Note to all - Must take a temporary break due to an upcoming trip out of town, but will be back online and providing further updates in a couple of weeks. Please stay tuned and continue helping me resurrect this beast! Appreciate everyone's patience. Thanks!
Thank you for all discussion. Gave me courage to go ahead and try to fix my SA 828. I loved my when working. It deserve all the hard working.
Congrats on joining the discussion Alexandre! Glad to see another SA-828 owner stepping up and deciding to try and fix their unit - instead of simply getting rid of it.
It really is a wonderful sounding piece of equipment when operating properly! With the dedicated help I'm getting from the experts on this forum, I'm determined to try and get mine fully functional again - and then take better care of it in the future to ensure it stays that way! I'll bet you can too!!
It really is a wonderful sounding piece of equipment when operating properly! With the dedicated help I'm getting from the experts on this forum, I'm determined to try and get mine fully functional again - and then take better care of it in the future to ensure it stays that way! I'll bet you can too!!
Hi Iceman,
I don't know when you will get the parts and when you will start reconstructing the unit.
I'm may be busy for a couple of weeks.
Let me remind you of the missing DCV measurements of IC601 !
The repair work should be done gradually.
Here are a few guidelines for the "1st phase of repair".
Disconnect all speakers from the bad channel!!!
Set volume to minimum(zero)!!!
Do not change theses settings unless specifically stated!
1.Check all parts on arrival to be good (Trs,Diodes,resistors),please tell what part numbers where supplied.
2.Clean VR601 and VR603 with Deoxit
work them all the way with a screwdriver( for a while when you spray them).
3.Solder all resistors.
4.Solder Trs up to and including Q621( do not insert Q623 and " higher")
5.Solder Diodes up to and including D613.
6.clean all solders well (a photo may be nice).
Measure the voltage between D607-anode (RED probe) and D609-cathode(black probe),
it should be about 4VDC,setting done with VR601 trimmer.
After that, set the voltage to minimum with VR601(what value is it?).
After that is done, the 2nd repair phase may be done.
I don't know when you will get the parts and when you will start reconstructing the unit.
I'm may be busy for a couple of weeks.
Let me remind you of the missing DCV measurements of IC601 !
The repair work should be done gradually.
Here are a few guidelines for the "1st phase of repair".
Disconnect all speakers from the bad channel!!!
Set volume to minimum(zero)!!!
Do not change theses settings unless specifically stated!
1.Check all parts on arrival to be good (Trs,Diodes,resistors),please tell what part numbers where supplied.
2.Clean VR601 and VR603 with Deoxit
work them all the way with a screwdriver( for a while when you spray them).
3.Solder all resistors.
4.Solder Trs up to and including Q621( do not insert Q623 and " higher")
5.Solder Diodes up to and including D613.
6.clean all solders well (a photo may be nice).
Measure the voltage between D607-anode (RED probe) and D609-cathode(black probe),
it should be about 4VDC,setting done with VR601 trimmer.
After that, set the voltage to minimum with VR601(what value is it?).
After that is done, the 2nd repair phase may be done.
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Thanks for the heads up, will try and follow your instructions to the letter. Appreciate detailed guidance. Have NOT yet tested voltage measurements of IC601, but will do so if you think it's a critical step.
Just to clarify, sounds like I install the components you mention in steps 1-6, then power it up to do the voltage check between D607 & D609?
Seem to recall VR601 is roughly in centered position right now - should I just leave it there to check initial voltage? Then check to see I can adjust to get approx 4 VDC? Then set to minimum and report voltage? Then power down & await further instructions regarding "phase 2" of the repair?
Just to clarify, sounds like I install the components you mention in steps 1-6, then power it up to do the voltage check between D607 & D609?
Seem to recall VR601 is roughly in centered position right now - should I just leave it there to check initial voltage? Then check to see I can adjust to get approx 4 VDC? Then set to minimum and report voltage? Then power down & await further instructions regarding "phase 2" of the repair?
K, thanks. Will try and accomplish IC601 voltage checks this AM. You mentioned using both 2VDC and 20VDC ranges, but my meter only has an auto-range function for DC volts, so presume it will accommodate whatever voltage it sees, correct?
Well, just checked voltages on IC601 and happy to report I didn't electrocute myself or burn up the board. Here are test results - hopefully good, but very pessimistic about Pin 1 reading (and I checked it multiple times just to be sure)...
IC601 (Red Probe to IC, Black Probe to GRD)
Pin 1 = -262 (can that be right? - NEGATIVE 262VDC?)
Pin 2 = 3.6
Pin 3 = 3.0
Pin 4 = -17(another NEGATIVE voltage?)
Pin 5 = .78
Pin 6 = 5.6
Pin 7 = 12.96
Pin 8 = 16.54
IC601 (Red Probe to IC, Black Probe to GRD)
Pin 1 = -262 (can that be right? - NEGATIVE 262VDC?)
Pin 2 = 3.6
Pin 3 = 3.0
Pin 4 = -17(another NEGATIVE voltage?)
Pin 5 = .78
Pin 6 = 5.6
Pin 7 = 12.96
Pin 8 = 16.54
Pins 4 and 8 should be about ±17V they are fine.
Pins 1,2,3 should be in the mV (milivolt = 1/1000 Volt ) range.
So no, -262V is not possible here,(now I understand why you said "electrocute myself"
)
Same for pins 5,6,7,but this is the bad channel which is now in "open loop" state,
so volts can be present.
Could you please note if the meter ranges to the mV range?
Pins 1,2,3 should be in the mV (milivolt = 1/1000 Volt ) range.
So no, -262V is not possible here,(now I understand why you said "electrocute myself"
)Same for pins 5,6,7,but this is the bad channel which is now in "open loop" state,
so volts can be present.
Could you please note if the meter ranges to the mV range?
Hmmm, hadn't thought about the possibility of the -262 being in the mv range (too busy watching probes to ensure no slippage). Will recheck and report back. Thanks!
Well, good news (I think)... You were a genius to suspect mv! Here are new voltage readings (now that I know I'm not dealing with hundreds of volts anymore and can study the DVM better without fear of getting juiced!):
Pin 1 = -259mv
Pin 2 = +3.7mv
Pin 3 = +3.0mv
Pin 4 = -17v
Pin 5 = +0.78v
Pin 6 = +5.6mv
Pin 7 = +12.96v
Pin 8 = +16.54v
What's the verdict on these new readings??
Pin 1 = -259mv
Pin 2 = +3.7mv
Pin 3 = +3.0mv
Pin 4 = -17v
Pin 5 = +0.78v
Pin 6 = +5.6mv
Pin 7 = +12.96v
Pin 8 = +16.54v
What's the verdict on these new readings??
Hmmm, got some strange readings when trying to do that. Grounded center pin of Z601 and initially got some very low values:
Pin 5 = +1.8mv (and rising)
Pin 6 = +4.3mv (and rising)
Pin 7 = +4.4v (and rising)
So then, after unit was powered on for a few minutes, checked again and got different readings (all negative values this time):
Pin 5 = -22mv (stable)
Pin 6 = -4.7mv (stable)
Pin 7 = -13.3v (stable)
What say ye?
Pin 5 = +1.8mv (and rising)
Pin 6 = +4.3mv (and rising)
Pin 7 = +4.4v (and rising)
So then, after unit was powered on for a few minutes, checked again and got different readings (all negative values this time):
Pin 5 = -22mv (stable)
Pin 6 = -4.7mv (stable)
Pin 7 = -13.3v (stable)
What say ye?
Good to hear, was not looking forward to replacing that additional component. Will continue to march based on your previously laid out battle plan. Thanks!
Hi! How have you been? Sorry it took so long to get back but you know how life can get in the way of things you'd much rather be doing lol. Well, I got the receiver working again and I've had it powered up several hours, several times, without fail. One thing I have noticed is that Q708, which is located on the riser board, is pretty hot. Do you have any idea how to deal with this. Thanks for your help. Here's a couple of pics of the happy patient : )
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