2270 Rebuild - Amp Board Transistor Question

A

acetate

Active Member
I tend to collect gear over the year and then rebuild over the holidays (my break from my full-time job). This year I have a bunch of 2270s sitting just asking for some attention. Two even have an engraved face. With my previous work on 2230s/1060s I have recognized the phono and preamp boards. However, the amp boards are quite different. Also based on reading a number of threads the amp sections seem to be the most failure prone. I will likely opt to just replace all transistors/diodes and electrolytics. I found a number of rebuild threads here for them but I was unable to find one of the recommended TO-39 replacements (2N5416/5415). Because of this I switched to TO-220 drivers (KSA940/KSC2073). I've read a heatsink wasn't necessary in other units but curious on thoughts for a 2270. Below are my planned swaps.

Location Original Replacement
H751 2SA640 ksa992fbu
H752 2SA640 ksa992fbu
H753 2SC945 KSC945C
H754 2SC735 2N3904
H755 2SC735 2N3904
H756 2SA484 KSA940TU-TO220
H757 2SC484 KSC2073TU-TO220
H758 2SC680 MJE15032
H759 2SA566 MJE15033
H760 2SC984 2N4921
H761 SM-150-01 1N4001
H766 2SA562 2N3906
H767 2SA562 2N3906

As a side note I did finally finish my complete rebuild of a Model 16 (internal and external). Pics and final notes will be coming closer to the holidays. I also plan a rebuild of a Model 33 to go with it. Again another post will follow soon on that.
 
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good luck with your 2270 rebuilds as it looks like you will be doing extensive work.

When I do a 2270 amp board I usually only replace the 945's the others seem trouble free.
 
I wouldn't just replace the transistors either honestly. I did contact Central Semiconductor who I believe is the last manufacturers of that 2N5415/6 a couple of moths ago. I got a response that they indeed still made them and would have them again soon. So far Mouser only has a minimum buy quantity listed that's a bit much for me to buffer buying a lot and reselling them. I'd be interested to hear from anyone who's swapped to the TO-220's.

Great model, my favorite really, it's well worth the efforts you'll put into it. Best wishes to you and we'll be watching for the progress. :yes:
 
I've come across plenty with shorted outputs but never one with a shorted driver. Maybe that TO-39 cased is a really resilient transistor to damage. I'd be interested in hearing from someone who has experience changing them since I know there will come a day.
 
Thanks guys. I will reconsider the all out replacement. I just did this on my 2230s and my 16 with good results. But either way I will want to put replacements on my order list since I have compressed times to actually do work. Finding a bad driver and not having the parts might make my head explode.

If anyone has changed to TO220 for the drivers please do chime in. I did find a fairly close TO39 replacement in 2N5680. Interested in input on that selection, if for nothing else than improving my transistor selection skills. The max current is less than the original but the same as the common 5416 replacement. Also the E-B voltage is lower but I'm thinking it would work. But it is almost $5/piece!

At this point I will probably add the TO220 to the order list with a couple heatsinks just cover myself. I did create a Mouser project with everything but the filter caps. Filter caps will be the Nichicon KGs 10k uf from PCX.

Right now my favorite is my 2215B (rebuilt). I do like the 2230s/1060s (rebuilt) though. With the help of this forum my first unit was a 2275 but it is unrestored. It has never really wowed me. Can't wait to get the 2270s restored. Also can't wait to get my 33 and 16 singing together.
 
For what it's worth, MJE243G will also work to replace H706 (2SC984) as will SD669 (hard to find, tho).
 
So I got all my parts in and finally got a good block of time to start this project. First unit I pulled was the engraved plate unit. I open it up and find the right amp completely disconnected (wires cut). :worried:

While it is easy I go ahead and replace the caps, 945s, and diff pair (heat shrinked together). I also opted to replace the filter caps since access is easy. I reconnect the amp board and bring it up on variac. No clicky click (relay). I find 42V at the relay post for the right amp (J757). I pulled the outputs, test, and they are hosed. I am also able to power the unit up with the outputs pulled and get that sweet clickety click. I pulled the drivers and tested them and they seem fine. I pulled most of the silicone and everything else tests ok.

Of course I didn't order these in my parts order (the only transistors) so I have a wait ahead of me. While I wait anyone else have any suggestions on areas to check?

The speaker posts are also in bad shape. I pulled one to get a look but it looks more difficult than slipping in banana jacks in my 1060. Anyone have any suggestions on an easy way to replace the speaker posts with banana jacks or some other post?

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I decided to pull the outputs from the left side and test with them. I really didn't want to risk an original set of outputs but I figure the variac will protect them. Anyways it powered up nice and gave me that special click. Audio sounded horrible and crazy loud staticy. So I swapped pre out/main ins to get the left preamp into right amp and it sounds nice. It seems the right preamp is bad and likely helped those outputs die on the right.

I will get an order in for some new outputs. Lots of hits on search for outputs and I am not finding an original datasheet to compare against. I'm seeing MJ15015/6 and MJ21193/4 as suggestions. It seems like the 1515/6 would suffice but I suck at this transistor matching business. Input appreciated.
 
I may have gotten confused about what you've done/not done, but your problem could well be in the caps on the amp boards (or the preamp section, for that matter). The electrolytics can fail (lead breakage) and cause the static problem. I just had that problem on an engraved 2270.
 
HVHiFI said:
MJ21193/94 work very well in the 2270.
Click to expand...

Thanks. I will get an order in today.

I am pretty confident that the issue is in the right preamp. If I cross the left preamp into the right amp then I get good sound. There is some crosstalk though. I also recapped the right amp board already (and changed out the 640s and 945s).

I will get some shop time later while the kids are at art camp. I will do a full rebuild on the preamp. It looked pretty similar to the 2230s/1060s preamps that I did over the fall so should go pretty quick.
 
I got the preamp completely rebuilt and the issues remained. Right side is totally distant, never turns off, never turns up, loud scratching when volume stem is touched. The left side has that same muted/distant sound when volume off but then starts to sound good as you increase the volume.

So I went at the controls with deoxit. Lots! I believe the volume pot is actually bad.

The right side gives loud scratching sound everytime the volume stem is touched. So I sprayed more and worked it more. But then I realized the stem is actually loose. I can turn off the sound completely with a gentle push on the volume stem. I don't think Marantz's had mute buttons back then. When peeking in through the slot I can see the internals rocking around when any pressure is applied to the stem. As luck would have it I actually have a spare (250k ohm x 2 with loudness tap from a 2275 (i think)) so I will try to swap it in later tonight or tomorrow.

The scratching sounds like a bad diff pair but only happens when the volume stem is touched.
 
Thanks Pat. I am still new at this so getting confirmation like this is super helpful that I what I'm thinking isn't crazy. Anyways, I got the new pot in today and sweet sweet music. All issues are now gone. Now I just need to finish the rebuild.

I'm still afraid to touch the tuner boards because of my fear of alignment. I have a Sencore SG-80 but haven't taken the time to learn to use it yet.
 
Lee is this true for all Marantz tuner sections? I was under the impression that caps could have a big impact. If not then I'll have at it.
 
acetate said:
The speaker posts are also in bad shape. I pulled one to get a look but it looks more difficult than slipping in banana jacks in my 1060. Anyone have any suggestions on an easy way to replace the speaker posts with banana jacks or some other post?

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Click to expand...

I recollect someone posted a pic of binding posts on the 2270, but
can't find it now. Somthing like this -

http://www.audiokarma.org/forums/showthread.php?p=6426167
http://www.audiokarma.org/forums/showthread.php?p=5134837
 
acetate said:
Lee is this true for all Marantz tuner sections? I was under the impression that caps could have a big impact. If not then I'll have at it.
Click to expand...

The electrolytic capacitors on the tuner boards are not critical for the alignment; they are mostly for DC filtering or the output high-pass filter. If you replace the small ceramic/film capacitors you will likely affect the alignment.
 
Do you have a 2270 silver engraved face plate in your collection? Looking for this model since i already have the champagne engraved 2270.
 
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