Akai 202D-SS blows main fuse

[Radioham]

Hi, I have a very nice Akai 202D SS that blows the main 2 amp power fuse immediately upon power up
.
I have isolated the lower preamp section from the upper mechanical section by disconnecting the large Molex plug on the right side. This leaves power to the lower section but not the top mechanical section. In that orientation the fuse does not blow and the preamps / headphone output work fine. Therefore I figure the problem is in the upper mechanical section correct? Please correct me if I am wrong on that.

Continuing on, all motors spin free and all mechanical linkage seems to be free. I am guessing that the problem should be in the capstan motor power section? Isn't that the only thing that would power on upon power up? I don't see anything obvious like blown caps or broken resistors. I have a service manual but don't know where to turn next.

Any suggestions would be greatly appreciated.

RadioHam - Myrtle Beach, SC

 

[audiojones]

It could be a shorted motor run capacitor although that's kind of an unusual failure for them (the ones I've seen fail usually go open). Could also be a shorted motor too but again that's not a very common failure. Before you isolate and test those possibilities I would take the faceplate off and take a look at all of the wiring and switch contacts behind there. I once had an X201D with the same problem, it turned out a screw for the mechanism behind the faceplate backed itself out and fell down between the chassis and the contacts for the "Auto Shut-Off" switch...POW!!

Look over all of the wiring harness from the mechanism plug through to all of the connections under the faceplate and back, there's lots of places for line voltage wires to get pinched and rubbed through and microswitch connections that can short if anything is loose inside. You might be able to use a dim bulb tester on it to verify that the short is cleared though you might need a bulb larger than 60 watts since its a motor load and not just an amp. The motor will spin slowly too, but at least you might be able to verify that the short is cleared if you find something suspicious. If you don't find something obvious under the faceplate then I'd probably isolate the capstan motor and run capacitor, check each for continuity to chassis ground.

 

[Radioham]

OK, here's an update. With the help of a dim bulb tester, (that I built just for this), I was able to isolate several problems. They all were in the CR-PC board, (MU-1007). I found and replaced a shorted capacitor, shorted diode and broken resistor. Now the unit no longer blows fuses, powers up and plays. Hallelujah right? Well, not so fast there tapeheads, now that I got the unit to power up and stay running, all these other problems surfaced. The unit plays forward only, will not reverse and the preamp is messed up. Only 1 out of four channels really works right. The other 3 are low or no volume. Now here's the real kicker. Its not even mine! I'm fixing it for a friend. I think I'm ready to give it back and say sorry, to many issues!!!! I was REALLY happy when I fixed the fuse issue but it all came crashing down when I saw how many other problems it has.

 

[audiojones]

Thanks for the update, it’s good to know where the power problem was. I’ve seen the 47uf 160 volt axial caps blow apart and the diode short on that board in other decks with this mechanism, it’s a PITA to get to.

I don’t know if it applies to this particular machine but often with 4 channel auto reverse decks the reversing function is locked out if you have the playback amp set to 4 channel mode. They do that so if you're listening to a 4 channel one direction tape you can’t accidentally hit reverse and hear half of it backwards. If you’ve got a stereo / quad switch on this model try it in stereo and see what happens.

Amp failure is common on all Akai decks due to the 2sc458 transistors they used in the amp section. Even if the schematic calls for a different transistor number you will usually find that Akai used the 458’s in the record and playback amps (and on the system control board too) and they cause all kinds of malfunctions. They can be replaced with commonly available KSC-1845 if you find them in there. Don’t bother testing them, they’ll test ok but crap out in circuit under real life conditions. Don’t know if it’s worth the trouble for you to repair but it’s not too big of a deal if you are used to component level repair.

EDIT: Of course thoroughly clean all of the switches and relay contacts first before digging into the amp boards (IF you decide to bother digging into it at all that is).

 

[Radioham]

OK, the saga continues! Here's another update: I cleaned all the slide switches and tried to clean the relay contacts, (what a pain there!), and had the following results. Now I only have one channel that's out. YEA! Front Right. The other 3 came up nice and loud after cleaning the slide switch contacts. Further inspection of the PB amp shows two 2SC711 transistors. This agrees with the schematics. TR1 is a 2SC1312. TR2 and TR3 are 2SC711. I think I need to replace TR3, it appears to be closes to the output on the schematic. So, in summary, I'm not exactly sure which TR to replace on the PB amp board, (TR1 TR2 or TR3?), and what to replace it with. (I did a little research and it looks like the KSC-1845 is a suitable replacement?)

Update on the reverse issue. I noticed there is a "muting" circuit in the schematics that mutes the audio output just long enough to allow the capstan motor to change direction. In the 2 channel mode, after pressing the reverse button, the audio does temporarily mute! So this part of the reversing system works but nothing else happens. With the switch in the 4 channel mode, there is no mute, indicating the reversing function is locked out as you stated. Interesting!

Thanks for your help, I'm making progress...…………!!!

 

[audiojones]

Oh one more thing I forgot to mention about the reversing system on that 3 motor transport; you must have the tape threaded properly around the right tensioning arm (the one right after the pinch roller) or the reversing system and the automatic stop mechanism won’t operate. There’s a microswitch on the end of that arm and when the arm is down the deck assumes the tape is not there.

The muting relay uses a time delay circuit triggered by the reversing contacts to mute the signal from the heads long enough for the flywheel to get up to speed. It also mutes on machine power up and when record is energized to prevent noise. That relay can cause channel dropouts too so I’d clean the contacts in it well plus I’d probably go back and clean all of the other contacts too before condemning the transistors (especially since its not using the typical trouble makers). Your reversing issue is most likely a dirty switch contact issue too, best to go back and triple clean / exercise all contacts and follow with clean compressed air. Sounds like this deck has been sitting for a long long time.

 

[Radioham]

Nightly update: Still having front channel right side playback issues with no sound. All other channels OK. I was fiddling around inside and noticed when power was on and playback engaged, (no tape), I did hear some hiss in the front right side thru headphones. Further investigation showed that when I put my finger on the input of the PB board for that front right side I got a hum and the VU meter went up. Ah Hah! That's the first time I saw or heard any activity there. I tracked the input wire back to the Front Record PC board and still had the finger noise there. So I guess the PB amp is OK? Seems like it. Also I tried recording. Never tried that before, always playback. When recording, all channels get sound thru the headphones and the VU meters work accordingly. That includes the front right channel that I am having trouble with. However upon playback all channels work EXCEPT that darned front right side. It wont play back what I had just recorded, (only on that front right side) even though I hear myself in the headphones and the VU meter shows my voice while recording. I took that same tape and put it on another deck that I know is good and it still did not play the front right side. So I guess recording and playback on the front right side don't work even though the VU meters show activity while recording, (nothing on playback - even when playing a prerecorded tape that I know is good). I thought it might be a possible bad head or wiring to the head. I tried the "finger" test again at the head and I get a hum and the VU meters work on all channels including the front right side that wont record or play. Its late and I'm tired so I will look into that tomorrow but right now I'm thinking bad head?

 

[Radioham]

. According to the service manual, (and I can see the heads), there is one full erase head, one 4 track erase head and ONE 4 track play / erase head.

Forgot to mention that I did try to clean the switches again. I completely removed and thoroughly cleaned the 2 / 4 track slide switch. I also tried cleaning the long slide switch on the front record PC board a second time. I will admit its a little hard to get to the opposite end of it so I will try it again. The other long slide switch is on the rear record PC board. I cleaned that too and that's how I got the other channels to work a few days ago. The only other slide switch that I know of that has anything to do with audio is on the Oscillator PC board. I have cleaned that once already but will clean it again. According to the service manual I believe that front and rear PB audio go through that board as well.

I did put my finger on the head wires. I kept the volume low and tried the finger test on the back of the head for the offending channel. I did get some hum -

Will advise again today after cleaning the switches again. Thanks!

 

[audiojones]

It could be the head but there's a quick and dirty test to find out for sure. Find terminal block J18 where all of the head wiring connects. With the deck playing a known good stereo tape (make sure it has music on both channels) take a paper clip or similar and short pin 3 of J18 to pin 1. This shorts the head output from the front left channel to the front right channel, and if you start getting a signal from both channels then you can rule out everything but the head and it's wiring up to the J18 terminal block. Don't rule out the connections on the J18 head connection terminal block either, if it's a removable plug it can have corroded pins. If all else checks out then I'd say it's likely to be an open winding in the head itself. Keep in mind that heads can be damaged by measuring continuity with volt meters.

 

[Radioham]

Ya know, I was just looking at that J 18 when I took a break and checked email. It is a removeable plug and I took it off and cleaned the contacts and reconnected, no luck. I did what you said, shorted pins 1 and 3 and I got the audio from the left side on both left and right. Both VU meters responded. I then shorted the same two pins but from one side of the connector to the other and got the same results. So its either the head or the short wiring run from the head to terminal block 18. Bummer.

 

[audiojones]

Yeah that's a bummer, sorry. If the reverse mode is working you can still play tapes on it in the reverse direction since it uses the other two tracks on the head for that function. Finding a good used quad record / play head isn't impossible, dunno if it's worth the trouble though (depends on the owner). FWIW that same 3 motor mechanical block is used on many many Akai decks so if you don't end up repairing it definitely keep it around, it might come in handy.

 

[Radioham]

Uh well...…..Don't know if I want to continue troubleshooting this unit. The reverse still doesn't work - even with all the cleaning. Wasn't quite sure how to clean the contacts in the reversing relay. I sprayed some contact cleaner on the contacts and exercised the relay back and forth. No luck. I considered putting a small piece of sandpaper in there and moving it around in between the contacts. As I said the muting function works when the reverse switch is pressed, that it.

 

[audiojones]

Well FWIW lack of reverse function isn't likely to be caused by dirty relay contacts. From what you've found it can be narrowed down to either a bad reversing relay coil, defective transistors in the reverse trigger circuit or bad / broken connection in the reversing circuit (assuming of course that you have the tape properly threaded through the tension arm so it is lifted up). Remember, if the right tension arm isn't held in the up position by the tape the machine will operate normally except the reverse can't be triggered and the auto-stop mechanism won't activate, it'll just keep going after the tape runs out (no automatic cam cycle unless the arm drops).

Anyway, sounds like you've gone way above and beyond trying to get this thing going again especially since it isn't exactly one of the greatest tape decks out there. Getting the reverse to work again shouldn't be too difficult but finding another 4 track combination play / record head may take a bit. Unless it has a great deal of sentimental value to the owner I'd probably shelve it.

 

[Radioham]

Its going back to the owner - as is. This tread is done. Thanks all.
Posting a new thread about a TEAC A1250 with slow playback.