Working on a Marantz 2325. No sound. Getting .4 to .5 volts DC going to relay board from audio signal. Relay board is in bad need of recapping but I have isolated the signal from the relay board and still .5 volts DC both channels. Does anyone recall this symptom on a previous repair? Thanks
Attached is best schematic I've found.
R713 is output offset pot. Insufficient adjustment range?
If this the case, please advise voltages at R713 wiper, C703, H702 base, L701 or other convenient output. Leakage in C703 is chief suspect but voltage readings will help confirm, or point elsewhere.
R713 is output offset pot. Insufficient adjustment range?
If this the case, please advise voltages at R713 wiper, C703, H702 base, L701 or other convenient output. Leakage in C703 is chief suspect but voltage readings will help confirm, or point elsewhere.
Base of H702 .83v and R713 .89v on one side of resistor-not sure which side is wiper the way its laid out.
I went ahead and replaced the 3 lytics on right side while I had out. With adjustment I was able to get it down to 50mv but its constantly changing dc voltage. it will be vely low ie 5mv then 20mv then 50 mv all within a second. The other side which I havent replaced caps is exibiting a simuliar pattern after adjustment but 5mv to 100mv. So the caps did help but not sure about the randomness of the DC.
Both channels with identical fault! That suggests a common cause.
Look for things common to both such as power supplies including any common regulated or Zener stabilised supplies (I haven't looked at the circuit). Definitely check all supplies before doing anything else.
Since you saw improvement with replaced caps, it seems they must have had leakage. Tantalums would probably have lower leakage than electrolytic.
Definitely look at +/- 20.5V rails for variation. If nothing is obviously suspicious with Zener supplies, try removing C703 as an experiment. It needs to be definitively eliminated from suspicion before looking elsewhere.
P.S. Please measure voltages at element ends of R713; to my eyes, the end terminal voltages don't appear to be well chosen for good adjustability. Looks like you'd likely run out of adjustment range.
Definitely look at +/- 20.5V rails for variation. If nothing is obviously suspicious with Zener supplies, try removing C703 as an experiment. It needs to be definitively eliminated from suspicion before looking elsewhere.
P.S. Please measure voltages at element ends of R713; to my eyes, the end terminal voltages don't appear to be well chosen for good adjustability. Looks like you'd likely run out of adjustment range.
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20 volt rail 20.7, -20 @ 20.57 both seem to be stable. I did previously replace C703 when I replaced the electrolytics on amp board. I used a Nichicon KL series since its a low leakage cap. Figured it would be next best thing to having a tantalum. R 713 is 3 volts on one end and now .9 volts since the cap replacements. I havent replaced the relay board caps. i had to order them. Mabye it would make some difference.
The R713 element voltages are about what I estimated-- and both higher than the 0.6V on H702 base. The result is that the pot will tend to force the output voltage to negative voltages; with nominal bias currents, the output offset voltage will never be positive and not adjustable to 0V. Is this what you observe?
If output remains erratic, I still advocate disconnecting C703 (and maybe C701) as a diagnostic test. If output remains erratic, I would begin to suspect transistor leakage (eg. H701, H702).
I wouldn't expect a relay board to have any effect on amp offset.
If output remains erratic, I still advocate disconnecting C703 (and maybe C701) as a diagnostic test. If output remains erratic, I would begin to suspect transistor leakage (eg. H701, H702).
I wouldn't expect a relay board to have any effect on amp offset.
P800 is board i'm refering to. Think it does more than just relay. The caps on it are shot- buldging and the relay is bad. I've got those on order. Plan on digging back into after they come iin.
Got caps in. The relay board does have problems of its own. Had assumed it was just bad relay & the buldging caps but still no relay function even if I unplug both sides of amp. Supply voltages are Ok on one side of board ie 35,20 but other side where relay is has off voltages. 50v at both sides of R817 and 50 and 0 instead of 1.2v on R816. I replaced the 3 transistors in that part of board but still no go. This thing is a doosie.
So what voltages are observed at J808 and J809 (i.e. switched relay contacts at L801 on board 800)?
As a sanity check, if you short H807 collector to ground, relay L801 should energize. (No load applied to speaker terminals to preclude damage.)
Assuming the relay does click, would you measure voltage to ground on both ends of R813 and R816? And R819 and R820. Try to measure directly on the resistor leads. Be on alert to possible open traces on PCB and poke around if things don't make sense.
Assuming the relay does click, would you measure voltage to ground on both ends of R813 and R816? And R819 and R820. Try to measure directly on the resistor leads. Be on alert to possible open traces on PCB and poke around if things don't make sense.
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Relay does click with sanity test,R 813 .003v on both sides R816 50Volt on one side and 0v on other. R819 and R820 less than a millivolt on all sides.
The problem sure seems to be on the relay board.
One possibility is R816 has opened. As a diagnostic, tie a 10K resistor from the hot side of R817 to the base of H806. This should inject about 5mA into base of H806. The larger test current should be enough to reveal where the fault lies. Confirm about 50V across the 10K resistor and measure voltage re ground at base of H806. Relay ought to enegize.
One possibility is R816 has opened. As a diagnostic, tie a 10K resistor from the hot side of R817 to the base of H806. This should inject about 5mA into base of H806. The larger test current should be enough to reveal where the fault lies. Confirm about 50V across the 10K resistor and measure voltage re ground at base of H806. Relay ought to enegize.
The resistor R816 was open. I had one in a resistor kit. Replaced it. Relay worked but burned new resistor in about 30 secs. It was the same size as old one.
Are you certain about R816 installed value? Should be about 50V across 390K. P=50*50/390K = 6.4mW. Smoke doesn't seem reasonable.
Yes it was 382k ohms-i measured before installing.. Im thinking whatever took out the first one mabye took out this one.