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Marantz 4300 Amps/Protection

GeezerB said:
Decided to have another look at this amp board... discovered that the trace was broken for the input on the rear part of the board! Started using a very simple signal tracer (just a cap with a small amp) and was amazingly easy to find that one... one good side. Was able to set offset and bias for that side.

Tried another amp board and although it initially allowed it to come out of protect, it would light the dim bulb after a little while so that one will need some attention. Thank goodness for the dim bulb.
Click to expand...
On this board that looked to be recapped aside from the diodes and the blue blob caps, I replaced both and it came out of protect! Rear channel works on that board. However, on the front board (with my signal tracer) I get signal up to H701 base. I do have 32V at the collector of that transistor, but nothing at the emitter. Even though that transistor tested good, I replaced them both (H701 and H702) with a matched pair, but still get nothing at the emitter?
 
GeezerB said:
I do have 32V at the collector of that transistor, but nothing at the emitter.
Click to expand...
Please check that voltage again. The schematic shows that you should have -34.2V at H701 collector (not +32V).
Check voltages at:
  1. H701 (c) = -34.4V
  2. H702 (c) = -34.4V
  3. H714 (c) = -37.0V
  4. H708 (e) = -34.3V
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That number is from the dim bulb so I will recheck straight from wall when I get back home to the unit.

Side note, I have taken the tip about color marking screen shots of schematics and it has been an incredible help to following these schematics
 
GeezerB said:
hat number is from the dim bulb so I will recheck straight from wall when I get back home to the unit.
Click to expand...
The DBT will not affect the polarity of the voltage. What I am concerned with is that you measured a positive voltage, not negative.
 
Understood, and I misspoke when I said 32 volts, the voltages are negative. This is on dim bulb.
H701C -32.66
H702 C -32.64
H714 C -32.74
H708 E hope I did this right... not sure how to access these so I measured from R731 which was -32.60 (looked like E connected to R731)
I don't know how to deal with that type of transistor package yet... the case measured -1.6

What I don't understand is that if there is a signal (can hear from signal tracer) at Base, and -32v at collector... shouldn't the H701 "turn on" and pass signal to Emitter? May be too much to get my head around, as I don't understand the H701/H702 pair
 
I did find an anomaly here in comparing the good side (rear) versus the non working side (front)
On the base of H702 I show -.8v DC... yet on the base of the other H701/H702 I show just a few mv.
Same goes for the other working side, and same goes for the other working board.

Could this be a contributing factor to it not working?
 
Have you tried doing this audio adjustment (again) after fixing your other problems?
Please measure and report the following voltages (don't adjust just yet):
  1. Connect your DMM (+) to #11 of J036(+) and (-) to #9 of J036(-) and measure the voltage.
  2. Connect your DMM (+) to #33 of J036(+) and (-) to #35 of J036(-) and measure voltage.
  3. Connect your DMM (+) to #13 of J036(+) and (-) to #15 of J036(-) and measure the voltage.
  4. Connect your DMM (+) to #31 of J036(+) and (-) to #29 of J036(-) and measure the voltage.
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I haven't adjusted anything, but here are the readings I currently have. I did also notice that the grounds (the strap that connects to bottom of amp heat sink) wasnt soldered on, I will do that ASAP
  1. Connect your DMM (+) to #31 of J036(+) and (-) to #29 of J036(-) and measure the voltage. .001
  2. Connect your DMM (+) to #33 of J036(+) and (-) to #35 of J036(-) and measure voltage. .001
  3. Connect your DMM (+) to #13 of J036(+) and (-) to #15 of J036(-) and measure the voltage. -.83
  4. Connect your DMM (+) to #31 of J036(+) and (-) to #29 of J036(-) and measure the voltage. jumping around like it is AC being measured from .1 up to 1.2V
 
  1. Connect your DMM (+) to #31 of J036(+) and (-) to #29 of J036(-) and measure the voltage. .001 (should be 12mV DC)
  2. Connect your DMM (+) to #33 of J036(+) and (-) to #35 of J036(-) and measure voltage. .001 (should be 12mV DC)
  3. Connect your DMM (+) to #13 of J036(+) and (-) to #15 of J036(-) and measure the voltage. -.83 (should be 0VDC)
  4. Connect your DMM (+) to #31 of J036(+) and (-) to #29 of J036(-) and measure the voltage. jumping around like it is AC being measured from .1 up to 1.2V (should be 0vDC)
The first three look like you can probably adjust to the correct value as described in the instructions, but the 4th one we will have to investigate further to see what is going on.
Looking back at my notes, it looks like that is the same channel that you had a problem with before where you had 35V on 25 and 35.
Do you still have the 36V on 25 and 35?
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Hi, no I got that straightened out, that was due to the white wire from Power Supply that supplied the negative 37V to the outputs having a bad connection, that I was able to fix and that phase of my problem was sorted out.
 
Correction to myself...
1st problem was that the white wire coming from Power Supply that supplied -36V had a bad solder joint, fixed.
2nd, actually had two output transistors blown (that I thought I had already checked out good, that was where I had 36V on 25 and 35), and that was fixed.

Now my issue is the high DC on the offset for both front and rear. I will solidify the ground and check and reflow all the joints, they look like good decent soldering but who knows. I do have the kit to replace H707-H710 and H714 to H716 as well, and new trimmers on order.
 
Redid the ground and now solid... just in case I did replace the aforementioned transistors. Trimmers test fine on the multimeter.

Still having the problem... H701 not passing sound to emitter and H702 has -.83 at base... trying to make sense out of it, but unable to.

The base of H702 has -.83... it looks like from the schematic that the following the base from H702 continues all the way to pin 13 (which goes to the base of H003 output) and has -.83

The trimmer has no effect...
 
Going to set this one aside for a bit and return when I have a bit more experience! Many thanks for the help so far.
 
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