This Aiwa AD-M700 Has Me Stumped. Could Use Some Help!

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Bloodhound

Bloodhound

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So long story short I've got an Aiwa AD-M700 I'm trying to resurrect. Fortunately I have a parts deck which has come in handy. Deck has been cleaned, lubricated and new belts have been installed. Also replaced the idler tire, RW/FF tire and take up reel tire. Switches have all been cleaned with deoxit and I'm good there. Here's the issue that has me stumped...

When playing from source input the sound is crystal clear and the VU meters don't skip a beat. When playing a tape the left channel goes in and out and the VU meter on the left dies out with it. I happened to touch one of the wires coming off the tape head with the tip of my screwdriver at the board end and the sound came back! Then it got staticky and went out again. Touched that wire with the screwdriver again and voila! Comes back for a minute or two then dies out. Right away I assumed it was a bad connection there so I resoldered it. No change and it's still doing it.

I know the connection is sound so what did I do by touching that wire with the metal end of the screwdriver to make it work? Did I alter the resistance somehow? Does this point to a bad cap on that side? This issue is with the left channel only.

Any help or advice is most appreciated. Thanks!200277547_1631159147074680_6979991727800031644_n.jpg
 
hopey

hopey

Member (SA)
It can be the small capacitor for the tape preamp circuit there is one for each channel. I have seen this on three different boxes easy to replace.
 
Hajidub

Hajidub

Member (SA)
Maybe a broken trace on the backside of the board where that wire connects. I doubt it'd be a cap if touching/moving the wire brought the channel back momentarily. Use a magnifier and look for a crack in the trace, since you already resoldered the wire (also reflow the head-side connection).
 
Bloodhound

Bloodhound

Member (SA)
It's a temperature related issue. I've determined that because it plays fine for a few minutes from a cold start and then dies. I removed the top and bottom covers and it played fine for 30 minutes straight before the L channel quit. I tried freeze spray and couldn't narrow it down. I also resoldered all the suspect joints I could with no improvement. Unfortunately it's beyond my ability to diagnose and repair. Not sure how to proceed since there's no reputable repair shops in this area.
 
Hajidub

Hajidub

Member (SA)
Freeze spray will work if it's transistor related.

BTW, something just came to me. I have 2 Aiwa's , GX-F66's that have (2) open top relays and both had a channel drop issue. Without looking at the schematic of yours (on hifiengine.com) Aiwa might have used similar relays. Deoxiting inside these relays brought my channels back and is a known issue. Sorry looks as though the thread pics from AK expired, I couldn't see them, but here's the link:
https://audiokarma.org/forums/index.php?threads/akai-gx-f66rc-intermittent-low-channel.485173/

Otherwise tapeheads.net had threads concerning the caps (as Hopey pointed out).

A hand bonk on top of the unit sometimes brought my channel back after a drop, until I deoxited the offending component. GL
 
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Bloodhound

Bloodhound

Member (SA)
After admitting defeat I sent the deck out of state for service. Turned out to be a bad orange cap in the affected channel. The tech did some extra work dialing everything in and this deck sounds amazing! It's now a permanent part of our Vintage Hi-Fi setup!
 
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