Had some time. Ran 3 jumpers to bridge cracked traces.
On power up - voltages stabilize - no drifting like before.
Bias is also correct. Used to take a few minutes to appear.
Pin6 IC101 4.44 / IC151 5.28
Emitter Q103 .589 / Q153 .583
Collector Q108 1.78 / Q158 1.79
Base Q101 fluctuates .000 .001
Q102 .002 / Q151 .003 / Q152 .006
Drop R114 .77 / R115 1.32 (same on other channel tho)
Drop R110 .68 (same on other)
DC at L output does slowly fluctuate between -001 and +001
If anyone has a blank board or even a stuffed one with nice traces, I'd be interested. My fixes may hold.
BL
On power up - voltages stabilize - no drifting like before.
Bias is also correct. Used to take a few minutes to appear.
Pin6 IC101 4.44 / IC151 5.28
Emitter Q103 .589 / Q153 .583
Collector Q108 1.78 / Q158 1.79
Base Q101 fluctuates .000 .001
Q102 .002 / Q151 .003 / Q152 .006
Drop R114 .77 / R115 1.32 (same on other channel tho)
Drop R110 .68 (same on other)
DC at L output does slowly fluctuate between -001 and +001
If anyone has a blank board or even a stuffed one with nice traces, I'd be interested. My fixes may hold.
BL
Hi Barry,
You know what I've done in the past? Take a picture or ten of the old PCB stuffed. Remove the parts from the PCB. Now you have a drilling guide. Cut a new PCB the same size and drill it. Clean the copper with steel wool and use the old board as a guide to .... connect the dots! Bluing ink works well. Lenline used to sell a PCB pen with bluing ink inside - works great. A black ink pen does not work well, you are further ahead with nail polish. Don't laugh 'cause it works.
Etch, clean and coat with solder (use flux first) as a plating. Reassemble and away you go.
I normally charge a couple hundred dollars for this as it's very time consuming. The customer ends up with an excellent repair.
-Chris
You know what I've done in the past? Take a picture or ten of the old PCB stuffed. Remove the parts from the PCB. Now you have a drilling guide. Cut a new PCB the same size and drill it. Clean the copper with steel wool and use the old board as a guide to .... connect the dots! Bluing ink works well. Lenline used to sell a PCB pen with bluing ink inside - works great. A black ink pen does not work well, you are further ahead with nail polish. Don't laugh 'cause it works.
Etch, clean and coat with solder (use flux first) as a plating. Reassemble and away you go.
I normally charge a couple hundred dollars for this as it's very time consuming. The customer ends up with an excellent repair.
-Chris
Hi Barry,
Add a diode drop (B-E, Q103) approximately to the voltage drop on R114 and you will be close to the voltage drop on R115. Perfect accuracy would give you a perfect match.
The IC output voltage is compensating for everything that can create an offset, including the offset created by the base current X R102 drop. This depends on the absolute value of tail current and transistor gain among other things. The designer knows the polarity of the offset and therefore supplies the op amp with the single supply in the direction of the correction required. Both channels are close to center very roughly so the designer knew what he / she was doing. ( I was taught that "he" stood for both sexes, some may take issue none the less)
It's not that bad if you just "nut up and do it".
K-amps,
Yeah I know. Might have charged more if I had the board to look at. But it's not that hard doing it my way. I've rescued several Marantz units (worthwhile) and a few other nice amps that way. Thinking back, I should have copied some!
-Chris
Add a diode drop (B-E, Q103) approximately to the voltage drop on R114 and you will be close to the voltage drop on R115. Perfect accuracy would give you a perfect match.
The IC output voltage is compensating for everything that can create an offset, including the offset created by the base current X R102 drop. This depends on the absolute value of tail current and transistor gain among other things. The designer knows the polarity of the offset and therefore supplies the op amp with the single supply in the direction of the correction required. Both channels are close to center very roughly so the designer knew what he / she was doing. ( I was taught that "he" stood for both sexes, some may take issue none the less)
It's not that bad if you just "nut up and do it".
K-amps,
Yeah I know. Might have charged more if I had the board to look at. But it's not that hard doing it my way. I've rescued several Marantz units (worthwhile) and a few other nice amps that way. Thinking back, I should have copied some!
-Chris
what you could do... is over the cracked traces, take a dremel at a slow speed with a 1000 or 2000 git sanding disk, and sand off the solder mask a bit till the copper trace is exposed, then carefully solder the crack with silver solder. if the trace is any more narrower than the thickness of a peice of laser jet printer paper folded 3 times, use some auto painters tape(thick masking tape) to cover any other exposed traces. then after all is said and done AND works, take a paint marker or some modelers paint,preferably the same color as the board or a differant color to mark the last cracks that you fixed, to paint were you soldered.
dremel bit: http://www.dremel.com/productdisplay/bit_template.asp?SKU=511&Color=660099
or
http://www.dremel.com/productdisplay/bit_template.asp?SKU=505&Color=660099
ive done this lots of times to remotes, small amps, just did it to an imac(well whats left of it any way), and various other things...
dremel bit: http://www.dremel.com/productdisplay/bit_template.asp?SKU=511&Color=660099
or
http://www.dremel.com/productdisplay/bit_template.asp?SKU=505&Color=660099
ive done this lots of times to remotes, small amps, just did it to an imac(well whats left of it any way), and various other things...
Excellent idea. Can do that on one of the cracks but there are now places (Q105/107/108) where the foil is missing
or partially missing from around the holes. Those areas look like they are almost "rotting". Have used cut resistor leads running from the transistor pins to a cleared spot on the trace. The work is quite neat and I have REALLY learned how to solder but my worry is how long these will last or how they will react to heat over time.
or partially missing from around the holes. Those areas look like they are almost "rotting". Have used cut resistor leads running from the transistor pins to a cleared spot on the trace. The work is quite neat and I have REALLY learned how to solder but my worry is how long these will last or how they will react to heat over time.
Flipped on amp this evening - DC offset is back - Got these measurements before offset "went away".
IC101 Pin#6 19.1vdc
C Q107/108 full B-
E & B Q103 full B-
B Q101 0.867vdc
B Q102 -3.71vdc
Started to get readings on Q105 and it stabilized.
Am (or maybe was) happy with the board and trace repair.
Everything is shored up as best as could get it. Doubt the above is due to cracked traces in the Q105/107/108 area but who knows. The witness resistors were not in. Have been turning it on / letting it run / turning it off / randomly / with a DVM on
C Q108.
BL
IC101 Pin#6 19.1vdc
C Q107/108 full B-
E & B Q103 full B-
B Q101 0.867vdc
B Q102 -3.71vdc
Started to get readings on Q105 and it stabilized.
Am (or maybe was) happy with the board and trace repair.
Everything is shored up as best as could get it. Doubt the above is due to cracked traces in the Q105/107/108 area but who knows. The witness resistors were not in. Have been turning it on / letting it run / turning it off / randomly / with a DVM on
C Q108.
BL
I realize this entire exercise shows me how little I know...
I may have found it. Again today powered on amp and measured.
No DC but sometimes it comes up OK and sometimes the left channel is "dead". No bias. Q105 off. Each time I would start to measure the usual: IC Pin6. Q101/102 emitter. Voltage drop across R114/115 and R108/110 and within "a few minutes" voltages would come back to normal. It wasnt the "few minutes" that was causing this - it was me touching R108 - the base of Q105.
When I had the DC yesterday - same thing - started to measure the usual - and a "few minutes" later everything would stabilize
(see post71 - I was at ..... Q105) I thought it was warm up or drift or something (pulling out what little hair I have left)
The problem was now repeatable. I could even touch R108 with a probe tip that was not connected to anything. Q105 would come on and the left side would power up. Cold solder joint or another cracked trace?.....covered both. No problems so far.
Unit is now under test.
BL
I may have found it. Again today powered on amp and measured.
No DC but sometimes it comes up OK and sometimes the left channel is "dead". No bias. Q105 off. Each time I would start to measure the usual: IC Pin6. Q101/102 emitter. Voltage drop across R114/115 and R108/110 and within "a few minutes" voltages would come back to normal. It wasnt the "few minutes" that was causing this - it was me touching R108 - the base of Q105.
When I had the DC yesterday - same thing - started to measure the usual - and a "few minutes" later everything would stabilize
(see post71 - I was at ..... Q105) I thought it was warm up or drift or something (pulling out what little hair I have left)
The problem was now repeatable. I could even touch R108 with a probe tip that was not connected to anything. Q105 would come on and the left side would power up. Cold solder joint or another cracked trace?.....covered both. No problems so far.
Unit is now under test.
BL
Hi K-amps.
The special order amp. Often looked at them and wondered. Never saw one installed. I understand they were a kit to make your Adcom into a vacuum cleaner (bagless).
I don't believe they would be of any use in a normal situation. Then there is the fan noise. Unpopular with the audio crowd for this reason.
-Chris
The special order amp. Often looked at them and wondered. Never saw one installed. I understand they were a kit to make your Adcom into a vacuum cleaner (bagless).
I don't believe they would be of any use in a normal situation. Then there is the fan noise. Unpopular with the audio crowd for this reason.
-Chris
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.