petehall347
the brandy coffee man
try swapping input rca cables to rule out external problem .
Model 27 with High DC Offset
- Thread starter Motnick
- Start date
Good point! I am using a recent yard sale find TT to test with which is completely unknown. Maybe it’s an issue with the cart. I swapped the rca cables. I’ll let it sit overnight and reevaluate in the AM.
mikepick
Active Member
Sort of the opposite of the problem I had where the sound in one channel would degrade to static after a period of use, turned out to be a failing transistor on the pre-amp board. You could probably track it down by checking voltages on startup vs. running for a couple of songs.
Does the same static problem happen with other inputs?
How is it sounding so far?
Does the same static problem happen with other inputs?
How is it sounding so far?
I went ahead and recapped the phono board. I reinstalled the metal shield over top of the phono board, and I also removed the tin foil that I had wrapped around the tuning string. I used the tin foil to protect the tuning string from my soldering iron.
I have not heard any more static from the phono board. Maybe the missing shield and the tin foil was causing some interference? I’m going to put some hours on the unit to see if the static returns.
This unit is sounding pretty good now. I think the owner of this 27 will be happy to hear his dads old receiver once again.
I have not heard any more static from the phono board. Maybe the missing shield and the tin foil was causing some interference? I’m going to put some hours on the unit to see if the static returns.
This unit is sounding pretty good now. I think the owner of this 27 will be happy to hear his dads old receiver once again.
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I think I found the issue. The bias in one channel takes awhile to come up to the 7mv setting after power up. It’s during this period that the left channel has the static issue. It seems I’m not getting consistent results with the bias pot in the one channel. I’m having a hard time getting the bias to return to 7mv after each warm up, and it takes awhile for this channel to climb up from zero after power up. Maybe I got the pot too hot during soldering?
The original bias pots were two legged. With the three legged replacements I had to solder the wiper to one of the legs in order to accommodate the PCB, but maybe I should have made a better choice when I selected the replacements. What’s the best choice for this?
This is what I installed as replacements:
652-3352W-1-102LF
The original bias pots were two legged. With the three legged replacements I had to solder the wiper to one of the legs in order to accommodate the PCB, but maybe I should have made a better choice when I selected the replacements. What’s the best choice for this?
This is what I installed as replacements:
652-3352W-1-102LF
petehall347
the brandy coffee man
capacitor charging issue or transistor flaky are my first thoughts . maybe heat and freeze spray is the way to go here .
What I notice is that in this channel some times I can only adjust the bias from 0mv - 3.5mv. At other times I have the full range.
Just a few minutes ago I had the 0-3.5mv situation and adjusted the volume up. The bias jumped up to 20mv and then I was able to adjust it back to 7mv even with the volume back at zero.
Maybe the volume pot needs more deoxit cleaning?
Just a few minutes ago I had the 0-3.5mv situation and adjusted the volume up. The bias jumped up to 20mv and then I was able to adjust it back to 7mv even with the volume back at zero.
Maybe the volume pot needs more deoxit cleaning?
petehall347
the brandy coffee man
bias diode ..H701 703 ETC
I lifted one leg of H701 - H704 during the previous troubleshooting and they tested fine with the diode tester on my meter. Maybe I should replace them?
Also wondering about the two caps that are involved C701 & C702. They are still original.
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petehall347
the brandy coffee man
yes they could do it .
petehall347
the brandy coffee man
change the pot first then . but you did that . so maybe the drivers are flaky .. i would do as i said earlier and use cold and heat to find the culprit .
testing with your meter is more like go no go testing . will find shorts and maybe leakage but wont test at operating voltages .
testing with your meter is more like go no go testing . will find shorts and maybe leakage but wont test at operating voltages .
Is the intention of this part of the circuit to control bias as the temperature of the power amp changes?
Excellent idea - added this to my tricks stash.
petehall347
the brandy coffee man
yes the vf changes with temperature
Jonstigator
Super Member
WOW! I hope I can read the resolve to this. I have a model 28 (no turntable ) I would like to restore.
I have ordered some freeze spray and I am waiting for it to arrive. While I wait I would like to identify some replacement parts for the temperature diodes and caps.
Would it be alright to use some film caps to replace C701 & C702? Perhaps these Panasonics 667-ECQ-E2224KB?
Can anyone suggest a sub for H701 - H704?
M8513-O
Would it be alright to use some film caps to replace C701 & C702? Perhaps these Panasonics 667-ECQ-E2224KB?
Can anyone suggest a sub for H701 - H704?
M8513-O
ncalsurfer
New Member
Wow, what an amazing thread! Thanks for sharing your process. I just picked up a Model 27 and can't wait to dive in. Thanks for being so detailed!
