2238B Restore

x2turbo

Well-Known Member
I'm in the process of restoring a 2238B. I'm replacing all the electrolytics to lengthen it's life and taking the shotgun approach of replacing all the transistors and zener diodes on the amp board because I could only get it to 28v when 35v is spec.

The amp board has definitely been worked on before and I have a couple of questions for those that know much more than me.

C164 is spec'd at 16v 220uf and I found a 16v 10uf installed. I returned it to spec.

Is this the general rule of thumb when one finds discrepancies? To put it back to spec? Or should I maintain the same cap since other parts that I'm not replacing may have been the reason behind the change.

There are a couple of caps installed on the bottom side of the board and by the amount of flux I'd say they weren't original.

First there is a 50v 47uf cap. It's connected between pin J739 and zener Q746.

A 200v 473m cap between pins J706 and J708

A resistor connecting the poles of the varistors, STV-3H (Q), Q741 and Q742 respectively. Note I'm not replacing these since I couldn't locate a replacement.

and finally a 100pf ceramic between pins J722 and J728

DSCN0436.jpg


DSCN0435.jpg


DSCN0433.jpg


Any thoughts on why these may be here?

Thanks
 
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Also, I haven't ordered the big caps yet. 50v 10000uf. Is there a recommended source for these that will match their size?
 
The amp board has definitely been worked on before and I have a couple of questions for those that know much more than me.

C164 is spec'd at 16v -220uf and I found a 16v 10uf installed. I returned it to spec.

Is this the general rule of thumb when one finds discrepancies? To put it back to spec? Or should I maintain the same cap since other parts that I'm not replacing may have been the reason behind the change.

Thanks

I think it depends on if you think the part in question is a production change or a factory service modification or not. It's not uncommon to find production modifications such as the parts soldered on to the bottom of the boards. These are often post production changes to solve problems that were identified after the units were in use in the real world.

You also have to take into account that the service manual or schematic may have the wrong part value listed. I have worked on some models that have what seem like obvious production installed components that do not show up anywhere in the manuals. I typically leave them as I find them.
 
There are a couple of caps installed on the bottom side of the board and by the amount of flux I'd say they weren't original.

I know mine is original, and it looks just like yours. :bigok:
 
I think it depends on if you think the part in question is a production change or a factory service modification or not. It's not uncommon to find production modifications such as the parts soldered on to the bottom of the boards. These are often post production changes to solve problems that were identified after the units were in use in the real world.

You also have to take into account that the service manual or schematic may have the wrong part value listed. I have worked on some models that have what seem like obvious production installed components that do not show up anywhere in the manuals. I typically leave them as I find them.

Thanks ChrisMarantz, what you say was kinda what I figured after spending most of the day under the hood. I've already found a couple of typos in the service manual. I also have to keep in mind if it was working before I starting replacing stuff then I'd probably be best served to replace it with what had it working in the first place.

and wouldn't you know that the cap under the board is the same value as the caps that I ordered incorrectly. I ordered a couple 50v .47uf instead of 47uf. I had a couple extra from a previous recap that went to fix the order mishap, but it left me without one for under the board. Certainly not the end of the world but what the heck are the odds on that? :scratch2:
 
Also, I haven't ordered the big caps yet. 50v 10000uf. Is there a recommended source for these that will match their size?

I think they are the 35MM, you may want to check. Parts Connexion has the Nichicon KG Gold Tune solder lugs 10000uf 50V. (35MM)
 
I finished replacing all the electrolytics and the transistors and the zeners on the amp board and I'm still only getting 27.5v instead of 35v. Good news is that I fixed the stereo light issue by replacing the HA1196 IC and wiring the light back to it's rightful location.

The following are the parts I replaced. I have not replaced the big power supply caps or Q735-736 (STD-04), Q741 -Q742 (STV-3H), Q747 (DS-131B) and Q748 (DS-132B). I plan on replacing the big caps but don't know of a suitable replacement for other parts.

Will replacing the power supply caps fix my voltage problem or is there something else I should check? For the record it sounds pretty good. Been playing it for a few hours with no issues.

ce07 10uf 35v 647-UKT1V100MDD
ce08 10uf 35v 647-UKT1V100MDD
ce09 4.7uf 25v 647-UKT1E4R7MDD
ce10 4.7uf 25v 647-UKT1E4R7MDD
ce23 1uf 50v 647-UKW1H010MDD
ce24 1uf 50v 647-UKW1H010MDD
ce25 3.3uf 50v 647-UKW1H3R3MDD
ce26 3.3uf 50v 647-UKW1H3R3MDD
ce27 1uf 50v 647-UKW1H010MDD
ce28 1uf 50v 647-UKW1H010MDD
ce35 220uf 35v 647-UFG1V221MPM
c154 100uf 16v 647-UFG1C101MPM
c163 1uf 50v 647-UFG1H010MDM
c164 10uf 16v 647-UKT1C100MDD
c165 4.7uf 35v 647-UKT1V4R7MDD
c170 100uf 16v 647-UFG1C101MPM
c172 4.7uf 25v 647-UKT1E4R7MDD
c208 4.7uf 35v 647-UKT1V4R7MDD
c210 22uf 16v 647-UKT1C220MDD
c211 .47uf 50v 647-UFG1HR47MDM
c217 1uf 50v 647-UFG1H010MDM
c218 1uf 50v 647-UFG1H010MDM
c301 4.7uf 35v 647-UKT1V4R7MDD
c303 100uf 16v 647-UFG1C101MPM
c304 3.3uf 25v 647-UMP1E3R3MDD
c305 1uf 50v 647-UFG1H010MDM
c306 1uf 50v 647-UFG1H010MDM
c307 .22uf 50v 647-UFG1HR22MDM
c311 10uf 16v 647-UKT1C100MDD
c312 10uf 16v 647-UKT1C100MDD
c313 2.2uf 50v 647-UFG1H2R2MDM
c314 2.2uf 50v 647-UFG1H2R2MDM
c317 .47uf 50v 647-UFG1HR47MDM
c318 .47uf 50v 647-UFG1HR47MDM
c319 4.7uf 25v 647-UKT1E4R7MDD
c320 4.7uf 25v 647-UKT1E4R7MDD
c321 100uf 16v 647-UFG1C101MPM
c322 10uf 16v 647-UKT1C100MDD
c401 2.2uf 50v 647-UFG1H2R2MDM
c402 2.2uf 50v 647-UFG1H2R2MDM
c407 22uf 16v 647-UKT1C220MDD
c408 22uf 16v 647-UKT1C220MDD
c411 47uf 16v 647-UFG1C470MEM
c412 47uf 16v 647-UFG1C470MEM
c415 2.2uf 35v 647-UMF1V2R2MDD
c416 2.2uf 35v 647-UMF1V2R2MDD
c421 100uf 50v 647-UFG1H101MPM
c422 47uf 10v 647-UFG1A470MDM
c701 3.3uf 25v 647-UMP1E3R3MDD
c702 3.3uf 25v 647-UMP1E3R3MDD
c705 47uf 16v 647-UFG1C470MEM
c706 47uf 16v 647-UFG1C470MEM
c709 47uf 50v 647-UFG1H470MPM
c710 47uf 50v 647-UFG1H470MPM
c719 10uf 16v 647-UKT1C100MDD
c720 10uf 16v 647-UKT1C100MDD
c721 10uf 16v 647-UKT1C100MDD
c722 10uf 16v 647-UKT1C100MDD
c729 220uf 50v 647-UFG1H221MHM
c730 47uf 16v 647-UFG1C470MEM
c731 220uf 10v 647-UFG1A221MPM
c733 470uf 63v 647-UKW1J471MHD
c734 100uf 63v 647-UKW1J101MPD
c735 33uf 50v 647-UFG1H330MPM
c737 100uf 16v 647-UFG1C101MPM
c738 10uf 50v 647-UFG1H100MDM
c739 1000uf 16v 647-UFG1C102MHM
c740 10uf 50v 647-UFG1H100MDM

q701 2sa750 610-PN4249
q702 2sa750 610-PN4249
q703 2sa750 610-PN4249
q704 2sa750 610-PN4249
q705 2sc1885 512-KSC2310YBU
q706 2sc1885 512-KSC2310YBU
q707 2sc1567 2sc1567 B&D
q708 2sc1567 2sc1567 B&D
q709 2sa794 2sa1249 B&D
q710 2sa794 2sa1249 B&D
q711 2sd388 863-MJ21194G
q712 2sd388 863-MJ21194G
q713 2sb541 863-MJ21193G
q714 2sb541 863-MJ21193G
q715 2sc945 512-2N5769
q716 2sc945 512-2N5769
q717 2sa733 512-2N3906BU
q718 2sa733 512-2N3906BU
q719-722 MV-13 512-1N4148 (2) wired in series
q723-734 1s2472 512-1N4148
q737 W06B 512-1N4005
q738 W06B 512-1N4005
q739 W06B 512-1N4005
q740 W06B 512-1N4005
q743 2sc945 512-2N5769
q744 2sc945 512-2N5769
q746 1s2471 512-1N4454
q749 W06B 512-1N4005
q750 2sc1885 512-KSC2310YBU
q751 2sc945 512-2N5769
q752 WZ-15C 526-NTE145A
q753 2sd330 2sd313 B&D

DSCN0442.jpg
 
I've had it playing all day and it's barely even warm. The bias and offset have held steady and the voltage rose to 28.5v. I've ordered new filter caps 10000uf gold tones. Hopefully that will resolve the low voltage issue.
 
I'm working on a 2238B also, have you changed out the transistors and zeners already? Is your parts list accurate for the trannys and diodes?
 
Yes I have changed out all the parts that are on my list above. Since I couldn't find a restore thread for a 2238b so I compiled my list by searching various other threads that used the same parts and gave recommendation for replacements. When I couldn't find recommendations I used datasheetarchive.com for info on replacements. Everything was from Mouser except for I reference B&D Enterprises. and I got the filter caps from parts connexion.

I'm not sure if the parts I listed above that I couldn't source a replacement are critical to the restore or not.

Not being able to get it to 35v is a bit troublesome though, but no one seems to have any tips for me to help me troubleshoot. :(
 
Not being able to get it to 35v is a bit troublesome though, but no one seems to have any tips for me to help me troubleshoot. :(

Are R786 and 788 good?
Have you cleaned R787 with FaderLube?
Measure the DC voltages on H750 and H751 with the black meter lead connected to the chassis.
H750
E 35V
C 52V
B 35.6V

H751
E 15V
C 35.6V (connected to H750 B)
B 15V

Tom
 
Thanks Tom for the advice.

I have not cleaned R787, didn't know that cleaning trimming pots was part of the process. I'll clean it now and give it some time and will report back on my findings.
 
Here's what I found

R786 - 21.88K (supposed to be 22K)
R788 - 15.13K (supposed to be 15K)

They appear to be good.

I lubed the trim pot R787 - retested voltage - 27.5v

H750
E 35v - 42.7v
C 52v - 48.8v
B 35.6v - 42.1v

H751
E 15v - 15.1v
C 35.6v - 42.8v
B 15v - 15.8v
 
I replaced all of the parts listed above including all the transistors except for the few parts I didn't know what to replace them with.

750 & 751 are listed here as H but should have been Q.
 
Q712 is part of that circuit, did you do it too? The wiring diagram shows 2 q712's, thinking it might be an error.
 
Yes I replaced 712 which i finally figured out was a typo for 718.

Keep the ideas coming.

Thanks
 
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