881 - Left Phono Channel No Bass

BrianPH

Member
So I just re-capped Equalizer, Tone, Driver and Power boards in my 881 and thought all was well until I just realized that when listening to records, the left channel is devoid of bass frequency content. I've ran both turntable outputs into the 881's R phono input and they both sound normal there, so it's definitely isolated to the L phono input. The FM and AUX inputs seem to be fine on both channels. So would troubleshooting need to begin with back of the L phono RCA jack? Anything specific come to mind that I should take a look at, on any particular boards? I think that I can follow the 881 schematic to trace the signal from the input but I'm no pro at doing so.

Thanks so much for you input!
 
Check your work thoroughly, and when you are sure it's all fine..... check it again.

'Equaliser' normally means 'Phono amp' - start there.
 
Does anybody happen to have a photo of the solder-side of their EQ F-2433 circuit board??? Looking at the back of mine and I'm seeing some things that look odd.
 
On the solder side of the EQ 2433 board there are two 220pF CEramic caps (C15, C16). One on the left channel the other on the right. However, on my board they are installed in two completely different locations on each side with respect to the other. Anybody know for sure where they go? I don't see them on schematic or the parts location diagrams but they are in the 2433 parts list.
 
Brian… Check for flipped caps (Lytics) cold solder connections…
If the LF is NOT making it through but HF is I'll wager something is wrong in the RIAA EQ section…..Where do you think the frequency cut off is? Above that "F" is the level down as well? Or is the balance ok.. just no BEEF in the left ?? Extra caps on the backside of sansui stuff , which is NOT on the print is VERY VERY normal.
 
Additional:
1) Verify you have +32 on pin 15 of the board AND it you get power to pin 1 of IC 01 THRU R 601 ( fuse resistor ) and R-07.
2) C-601 C-07 C-03 CO-01 are not flipped.

3) Do you have access to a scope ?
4) Hmmmmm interesting C 602& C-707 Keeps the phono section floating off ground..
Use an ohm meter and verify the phono jack ( s) are not tied to ground.
5) did you REALLY clean the input select switch ??
 
Thanks a million for your input, Vigman. I'll check these things immediately upon arriving home and report back.
 
I get 46.2vdc at pin 15 and 2.4vdc at pin 1 of IC01. Cap orientations look accurate. I don't have access to a scope. All switches were cleaned with deoxit gold.
 
Additional:
1) Verify you have +32 on pin 15 of the board AND it you get power to pin 1 of IC 01 THRU R 601 ( fuse resistor ) and R-07.
2) C-601 C-07 C-03 CO-01 are not flipped.

3) Do you have access to a scope ?
4) Hmmmmm interesting C 602& C-707 Keeps the phono section floating off ground..
Use an ohm meter and verify the phono jack ( s) are not tied to ground.
5) did you REALLY clean the input select switch ??



Are my voltage readings of any concern??
 
Yes, use the working channel as your cross reference....
I assume your 46.2 +VDC is against ground... ?
2.6 volts @ pin 1??!! Me thinks you have a resistor open in the B+
 
Yes, use the working channel as your cross reference....
I assume your 46.2 +VDC is against ground... ?
2.6 volts @ pin 1??!! Me thinks you have a resistor open in the B+

So I get 45.4vdc at pin 15 on the EQ board and at point 14 on the 2437 power board. Both should be 32.5vdc. So that means possibly a bad resistor on the 2437 power board? Doesnt the B1 that feeds the left phono channel at point 15 also feed the right phono channel at point 16.... is this B1 issue not necessarily the cause of the left phono channel issue?
 
I looked at the print again ( with a fresh cuppa joe ) ….
Pin 1 SHOULD be ~ 2.1 volts ( odd )
and NOW measure pin 5 should be ~ .7 volts above gnd.

Confirming on the OTHER side of R-601 you have ~32 volts ??

Verify your 330K ( R-07 )
AND
R-17 820 ohm

Rob , zeners way down stream
 
Seriously guys....I really appreciate your willingness to help. Without your guidance I'd be sitting here with a useless device. I'll make more investigations once home tonight.
 
I looked at the print again ( with a fresh cuppa joe ) ….
Pin 1 SHOULD be ~ 2.1 volts ( odd )
and NOW measure pin 5 should be ~ .7 volts above gnd.

Confirming on the OTHER side of R-601 you have ~32 volts ??

Verify your 330K ( R-07 )
AND
R-17 820 ohm

Rob , zeners way down stream


Left channel pin 5 = 10vdc, right channel pin 5 is .637vdc. So left channel is definitely out of spec

Regarding R601, on the pin 15 side its 45.6vdc but on the pin 16 side its 31.5vdv

For R07 and R17, how can I verify? Can they be tested in circuit? I don't seem to get a reading when I test them.
 
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The lower half of the EQ board is more or less symmetrical, like a mirror image except for the locations of that ceramic capacitor.
 
What is that dark green/black thing next to the left hand ceramic capacitor?

If the dark green thing is also a capacitor, it looks like there should be 2 pairs of capacitors on the underside of that board? - meaning there is one capacitor missing perhaps?
 
Gah my eyes

OK…
There is a LOT of solder spittle & rosin & pieces of Jimmy Hoffa on the board That needs to be clean.

Ive annotated area's that are a bit SHADY….

Like John, I also have the WHAT THE HECK IS THAT circled.

Verify your 330K ( R-07 )
AND
R-17 820 ohm

This circuit is simple enough you " shouldn't " need to pull em.

So me a pix of your meter
 

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