2245 One Channel Low and Distorted

grey_beard

Active Member
I've got a 2245 opened up and it needs some work. The first thing I want to get figured is a bad channel.

I have signal generator and oscope but I'm not very familiar with the schematic so I thought I would reach out for some help tracking down the issue.

I've deoxited the pots and switches. No luck.
I took the preout to another amp and the distortion is still there. So I guess that means it's before the amp board. Correct me if I'm wrong.
Low channel and distortion is on the right side, left is clear and strong.
Distortion is present using headphone jack as well as speakers.

I have the schematic and service manual.

I'm hoping someone can help me check voltage in some key places to track down the issue.

Thanks in advance,
Gary
 
Try Input a 1kHz signal into AUX input and check the quality of the waveform going into the Preamp board and compare to it’s output. There are some phone apps now that will generate a tone. That should pinpoint if there is a bad transistor or cap on the Tone board. Then you can try to drill down following the signal path or pull and check each component. At that point might as well rebuild the board. If it looks good In and Out then something further down the line like speaker switch, Vol pot or relay. I’m not an expert but have been learning over the years. Thanks especially to support found here. Do you need specific points to check?
 
Try Input a 1kHz signal into AUX input and check the quality of the waveform going into the Preamp board and compare to it’s output. There are some phone apps now that will generate a tone. That should pinpoint if there is a bad transistor or cap on the Tone board. Then you can try to drill down following the signal path or pull and check each component. At that point might as well rebuild the board. If it looks good In and Out then something further down the line like speaker switch, Vol pot or relay. I’m not an expert but have been learning over the years. Thanks especially to support found here. Do you need specific points to check?

That’s what I’m trying to do, I just need to know what points to check and what to expect at those points.
 
I'm tracking this down some this morning. Here's what I'm finding.

I've tracked signal coming into P400 Tone Amp board and the signal is good coming in, but bad on the right side going out. I'm able to compare voltages against the left side which is good.

The signal looks to be bad at H405 so I took the voltages with it attached to the board and it looks to me like the voltage coming into it is too high.
Here are the voltage readings for H405: B: 1.1, C: 0.7, E: 0.5 . Compared to H406 which measures B: 0.9, C: 12.4, E 0.3.

If I'm reading the schematic correctly it looks like the voltage at the base of H405 is too high and the collector is way too low.
 
Took some more readings around H405 and found R422 looks to be bad. Measured on board from board ground and have 28.4v on one side and 1.1v on the other. If I'm reading the schematic correctly it should be 0.85v where I have 1.1v.

R423 has 28.4v and 0.85v which looks right to me.

Does anyone have any insight on this? Any reason not to replace this resistor at this point? And, what resistor would I replace it with? I see that it is 2.2 Megohm .25%, but I'm not sure how many watts.

Thanks.
 
Last edited:
I'm tracking this down some this morning. Here's what I'm finding.

I've tracked signal coming into P400 Tone Amp board and the signal is good coming in, but bad on the right side going out. I'm able to compare voltages against the left side which is good.

The signal looks to be bad at H405 so I took the voltages with it attached to the board and it looks to me like the voltage coming into it is too high.
Here are the voltage readings for H405: B: 1.1, C: 0.7, E: 0.5 . Compared to H406 which measures B: 0.9, C: 12.4, E 0.3.

If I'm reading the schematic correctly it looks like the voltage at the base of H405 is too high and the collector is way too low.

Looks like your not getting the 12.5v at collector of H405. That a bigger issue. 1.1 vs .85 is not that far off. Suspect R428 (10k ohm) or C410 (3.3 if). What if resistance across R428? May need to lift one leg. And pull C410 to measure capacitance.
 
Looks like your not getting the 12.5v at collector of H405. That a bigger issue. 1.1 vs .85 is not that far off. Suspect R428 (10k ohm) or C410 (3.3 if). What if resistance across R428? May need to lift one leg. And pull C410 to measure capacitance.
Compare voltages on H407, H408 E as well. Can measure on that side of R428, R429.
 
r428 measures 10K on the nose.

h405 collector is only .67v.
h406 collector is 13v.

So where does the voltage for h405 come from? R426. Which is giving off just .67v.
Backing up from there. R428 is giving off just 1.344v versus R429 which is giving 13.5v.

Looks like R428 needs to go.

Does that sound right?
 
If R428 is 10K ohms is good. Check for cold solder joint on back side. Also check R426 which delivers the 12.5v to H407 Base. Resistors are usually less likely to fail vs. 45 yr old capacitors and transistors.
Then I would focus on C410 or C414. One of those could be bad and pulling down the 12.5V. Check voltage at connectors J412 compared to J411. And J405 vs. J406.

Does your DMM have capacitance checker? If not, I would probably replace those 2 caps. Or you could swap them with the other side. (C411, C415) and see if problem moves to the other side.
 
What do you think about h405 and h407? I'm trying to figure out where I'm losing voltage.

r428 is good but the voltage on one side is too low which to me says either h405 or h407 could be bad.

Unfortunately, I can't seem to locate a parts list for this particular board. The page is missing from all of the online versions I've found.

Input???
 
The 2270 is the same as well as the 2230 I believe.

These should get the job done.
Note: The BJT component numbers are listed on schematic borders above or below their board sections or you have to read directly on the device with a magnifying glass.
H403, H404, H407, H408: 2SC493 >>>> KSA992 Mouser #: 512-KSA992FTA
H401, H402, H405, H406: 2SC1000 >>>> KSC1845 Mouser #: 512-KSC1845FTA
 
Might as well do the caps while your there if feeling adventurous.
Here is a list of Mouser #'s I have for the P400. Just not crossed to the cap number. Would have to cross it yourself.
The are all Panasonic Films and UFC's. Many folks here prefer the Wima's as well which are a bit more pricey.
# P400 Tone Amp
667-EEU-FC1V101 1
667-EEU-FC1H100L 2
667-EEU-FC1H3R3 4
667-ECQ-V1H105JL 2
667-ECQ-V1H105JL 2
667-ECQ-V1H474JL 2

Here's another list with digikey part numbers, you can cross the mfg. number to Mouser if needed.
P400 Tone Amp
Radial
1 100/35 USE P10294-ND CAP ALUM 100UF 35V 20% RADIAL
2 10/35 USE 10/50 P11250-ND CAP ALUM 10UF 50V 20% RADIAL
4 3.3/25 USE 3.3/50 P10314-ND CAP ALUM 3.3UF 50V 20% RADIAL
2 1/35 USE 1/50 stacked film P4675-ND CAP FILM 1UF 50VDC RADIAL
2 1/25 USE 1/50 stacked film P4675-ND CAP FILM 1UF 50VDC RADIAL
C401, C401 2 .22/50V Use Panasonic ECQ-V1H224JL

This is a classic 2245 Restore Thread by PatFont.Lot's of great ideas in here...
http://audiokarma.org/forums/index....really-nice-rebuild-marantz-2245-2270.477423/
 
I am not opposed to recapping the board or even the whole amp, what I don't want to do is order up a bunch of parts and find out that the issue was a $.25 transistor.

I'm still trying to make sense of the schematic around h405.
 
If memory serves me correctly, the silkscreen labels for H401, 402, 403 and 404 are all messed up on the 2245/2270 tone board. Spend some time studying the labels and remember odd numbers are on one side of the board and even numbers on the other. In other words, H401 and H402 should not be next to each other.
 
I'm back to thinking that it may be a problem with H405. When I put a waveform through the amp the first place I see distortion is on the collector leg or H405.

What do you folks think? What are the chances that a bad transistor is causing this?
 
Very likely based on your checking the other passive components are good. Go for it. I was thinking since have to pay shipping might as well get the items needed to do additional upgrades when you are ready.
 
Back
Top Bottom