2215b Amplifier board repair - From no sound to distorted sound - help?

TravAndAlex

Active Member
So I've had a 2215b sitting on a basement shelf for a couple years. Picked it up broken inexpensively because it made no sound. Tested the preamp section by terminating the 3 conductor cable to the amp board to RCA jacks temporarily and all seems well with that half of the equation.

Tested all resistors and they appear to be within range.

Figured I'd just do a reasonably major overhaul of the amplifier board to see if that fixes things. Partial success. It plays but sounds almost as if the gain is too high. Played softly it is reasonably clear, but when turned up the bass is very distorted. Wondering if anyone knows what might be the culprit?

From another thread, here are the replacement transistors I used:

701/702 KSA992FBU
703/704 KSC2690AYS
705/706 KSC1845FTA
707/708 KSC2690AYS
709/710 KSA1220AYS - original thread recommended KSA1220YSTU but as they were not available, the thread suggested the KSA1220AYS as a replacement.

MJE15030 (NPN) for the D313
MJE15031 for the PNP B507D

Details from my order:

2 KSA992FBU-ND TRANS PNP 120V 0.05A TO-92

2 KSC1845FTACT-ND TRANS NPN 120V 0.05A TO-92

4 KSC2690AYSFS-ND TRANS NPN 160V 1.2A TO-126

2 KSA1220AYSFS-ND TRANS PNP 160V 1.2A TO-126

2 MJE15030GOS-ND TRANS NPN 150V 8A TO220AB

2 MJE15031GOS-ND TRANS PNP 150V 8A TO220AB

6 493-11035-1-ND CAP ALUM 100UF 20% 35V RADIAL

2 493-15143-ND CAP ALUM 47UF 20% 50V RADIAL

2 493-3181-ND CAP ALUM 2200UF 20% 35V RADIAL

4 EF1105-ND CAP FILM 1UF 10% 100VDC RADIAL

Before and after pictures:

IMG_6184.jpg IMG_6186.jpg IMG_6183.jpg IMG_6185.jpg
 
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gotta scope?

if so, for grins, inject Mr 150mv, 1khz signal into the aux/tape in and with the finals out of the picture, show us the trace as you increase volume? at the driver stage outputs...which (not having my sm in front of me) are the 1220/2690 pair?
 
gotta scope?

if so, for grins, inject Mr 150mv, 1khz signal into the aux/tape in and with the finals out of the picture, show us the trace as you increase volume? at the driver stage outputs...which (not having my sm in front of me) are the 1220/2690 pair?

Unfortunately no scope at this point. :(
 
I assume you redid/checked the bias after the TR replacements.
General health of caps appear OK
 
Did you test any of the parts you removed? If any of the transistors are bad there may be some resisters that went south at the same time.

Tony
 
I assume you redid/checked the bias after the TR replacements.
General health of caps appear OK

I did. Measures 0.010v across R735 and R736 after adjusting R727 and R728. One was at 0.07 and the other was 0.09 before adjustment.
 
Did you test any of the parts you removed? If any of the transistors are bad there may be some resisters that went south at the same time.

Tony

Unfortunately, I did not, and as I pulled parts I just dropped them all in a bag. No way to tell what was where originally anymore. I did test the resistor values before doing any changes and all seemed in order.
 
Any work done on power supply?
If both channels affected then look at power supply. Measure voltage at pin J706 on main amp board.
Maybe the psu can only deliver modest amounts (=quiet playing). Main caps replaced?
 
Any work done on power supply?
If both channels affected then look at power supply. Measure voltage at pin J706 on main amp board.
Maybe the psu can only deliver modest amounts (=quiet playing). Main caps replaced?

I haven't touched any of the other boards. Worth a try! I'll report back.

On second assessement, it is fairly distorted at anything but the quietest of volume.
 
Ok, I did one of these late last year and they aint too hard to ferret out....

here is what I would do:

a) tune it to a strong fm station and feed tape out to tape or aux in on some other machine.
if not distorted then we know its on p700, if distorted then that is a whole other bucket of worms.

b) remove transistors 711-714 inclusive and listen on headphones (yes, the drivers will power them just fine) distorted?

answer those questions while I peek some more at the SM...

added: have you done anything to board PE01?

added: nothing about your sub lists sucks and nothing stands out to me as a no no, when I get some time I need to see the routing thru PE01 - is it non-deafeatable?

and did you even try to set the bias at all? I would err on the side of LOW right now...
 
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I had some time to tire my eyes on the SM from hifi. It appears that all roads lead thru the PE01 tone/preamp board

well there appears to be 6 pieces of silicon in there that if I am not mistaken, all resolve to modern KSA992s and KSC1845s

at what, 20 cents each, match up a batch such that you have 6 with identical or near to it HFE, npn vs pnp, left vs right and glue those in.

keep bias out of the picture for now, WGAS about crossover distortion, it sounds like you have 'half the friggin signal missing' distortion. Or so I guess.

I would however, at this time ask more firmly what someone asked before, did you peek at the power supply? does it supply what is advertised? In my scant marantz history, I have found that the PS's oft spec caps at or near the max voltage - no room for wiggle and here we are 40 years later. take every 16 and make it a 25, every 25 and make it a 35, replace any of the diodes

H802-805 find (U05B 100pi, 2.5amp) look up something from mouser 3 amps and the voltage is about guaranteed to be higher, for H806-807 (150v .75a) can be swapped out for a 1n4004 (400v 1a) or 1n4005 (600v 1a) and the WZ140 zener (14v 500mw) can be had with a 1N5244B. H801 the power trans, well find something better than 1W 1.5A Ic mebbe in a larger case you can sink?
 
Hi Guys. Sorry for the long time before a reply - finding time for projects is proving challenging but I do have a few minutes today. I appreciate the help!

Any work done on power supply?
If both channels affected then look at power supply. Measure voltage at pin J706 on main amp board.
Maybe the psu can only deliver modest amounts (=quiet playing). Main caps replaced?

Voltage at pin J706 on the amp board is: 52.2v DC (to ground). Is there a list of voltages on pins somewhere for this receiver? I don't see it in the service manual.

I have done nothing to any board other than the amp board.

Ok, I did one of these late last year and they aint too hard to ferret out....

here is what I would do:

a) tune it to a strong fm station and feed tape out to tape or aux in on some other machine.
if not distorted then we know its on p700, if distorted then that is a whole other bucket of worms.
Hooked it up to another amp and things seem fine coming out of the Tape Out. No distortion.

b) remove transistors 711-714 inclusive and listen on headphones (yes, the drivers will power them just fine) distorted?
Haven't had a chance to pull those transistors yet, but headphones appear to play fine.
answer those questions while I peek some more at the SM...

added: have you done anything to board PE01?
I have done nothing to any board other than the amp board.
added: nothing about your sub lists sucks and nothing stands out to me as a no no, when I get some time I need to see the routing thru PE01 - is it non-deafeatable?

and did you even try to set the bias at all? I would err on the side of LOW right now...

I did. Should I set it lower?
I did. Measures 0.010v across R735 and R736 after adjusting R727 and R728. One was at 0.07 and the other was 0.09 before adjustment.

keep bias out of the picture for now, WGAS about crossover distortion, it sounds like you have 'half the friggin signal missing' distortion. Or so I guess.

I would however, at this time ask more firmly what someone asked before, did you peek at the power supply? does it supply what is advertised? In my scant marantz history, I have found that the PS's oft spec caps at or near the max voltage - no room for wiggle and here we are 40 years later. take every 16 and make it a 25, every 25 and make it a 35, replace any of the diodes

H802-805 find (U05B 100pi, 2.5amp) look up something from mouser 3 amps and the voltage is about guaranteed to be higher, for H806-807 (150v .75a) can be swapped out for a 1n4004 (400v 1a) or 1n4005 (600v 1a) and the WZ140 zener (14v 500mw) can be had with a 1N5244B. H801 the power trans, well find something better than 1W 1.5A Ic mebbe in a larger case you can sink?

Thanks for the parts suggestions! I can order things and redo the power supply. Do you know what voltages I should be measuring at what pins?

In playing around some more, it appears that the distortion really only presents itself with low frequencies. Disabling loudness reduces the distortion considerably (basically unnoticable on a strong FM station).
 
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Voltage at pin J706 on the amp board is: 52.2v DC (to ground)
SM has 53V on H711, H707 Collectors, so OK

Haven't had a chance to pull those transistors yet, but headphones appear to play fine.
If no distortion through headphone at moderate/high volumes then clean/deoxit speaker selector. Try connecting spkrs to Speaker B.
Headphone output comes from the power amp so this would rule out preamp/power amp as the cause.
 
SM has 53V on H711, H707 Collectors, so OK


If no distortion through headphone at moderate/high volumes then clean/deoxit speaker selector. Try connecting spkrs to Speaker B.
Headphone output comes from the power amp so this would rule out preamp/power amp as the cause.

I liked the idea! Unfortunately no improvement after a liberal deoxiting and testing on Speaker B. :(

Also, just double checked with a different pair of headphones and speakers. Still distorted bass through the speakers and not through the headphones at moderate-loud levels.

After giving the SM a serious look, I found the power ratings on Figure 14 for the Power Supply Assembly P800 board. Here's what I've got (it all seems fine - slightly higher than listed):

Using J809 as negative:
J808 52v listed: 52.4v actual
J811 33.7v listed: 34.1v actual
J813 14v listed: 14.2v actual
J814 10v (7.3v) listed: 10.2v actual
 
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Those voltages are fine. just make sure you recap power with uprated voltages and recap the PE01 board
 
Played softly it is reasonably clear, but when turned up the bass is very distorted

If this is the "only" distortion and it's occurring on both channels and headphones sound reasonable then the amp may only be able to provide low/modest amounts
of power. I would have to agree with quaddriver,
ust make sure you recap power with uprated voltages and recap the PE01 board
.
I would focus on the P800 and use Nichicon KW and PW but that's a personal choice. Due to its age, the whole Rx needs to be recapped. Doing
PE01 would provide a noticable improvement.

Suggest recap P800 and see how it sounds.

The power feed for the power amps (53V/J706) comes from the main filter cap c803. If this cap has deteriorated due to age...
 
Dagnamit. Just changed all the electrolytic caps on the power supply board. No improvement.

Should I be concerned: the manual states a 220 uF at C808, but there was a 100 uF in that spot. I changed it to the 220. Will this cause any issues?

IMG_6451.JPG
 
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Should I be concerned: the manual states a 220 uF at C808, but there was a 100 uF in that spot. I changed it to the 220. Will this cause any issues?
C808 is for the phono and tuner power supplies. It's not the cause of the distortion. I like the 220uf in that position, I don't see any issues.
 
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