Tascam 488 mkII bus 2 record issues!

N

notbillcosby

Member
After gushing about my 488 mkII to my buddy forever and ever, he finally got one. It won't record to tracks 2 and 6 on the tape though! Let me elaborate:

*I've played a tape in the machine that has sound on all 8 tracks. All 8 play back fine, through the tape cues as well as the channels on the mixer.

*When routing a signal from a mic to bus 2, there are no issues. If you arm tracks 2 or 6, the VU LEDs light up and show that signal is happening.

*If you try recording to tracks 2 or 6, nothing prints to the tape unless the signal was really loud. If you were loud enough, the peaks play back in a gross crackly low quality way but the quiet stuff still isn't there.

*I've only tried this with DBX on.

I'm not an electronics champ, but I'm good at soldering. Seems like maybe a cold solder joint or something.... any ideas?
 
My buddy said he cleaned them and they didn't look bad to my eyes. Seemed curious that both tracks 2 and 6 would have issues, especially since they're both sharing a buss. Do I have my terms right on this?

Although, it's obviously ALMOST working, if I can get the VU's to respond when tracks 2 or 6 are armed, and they alllllmost record if you're super loud. Maybe we can give another good scrub with the ol' isopropyl and give it another demag...
 
Really? No one knows what solder joints to check or anything? There's no hospitals around here, only my workbench and soldering iron downstairs...
 
notbillcosby said:
Really? No one knows what solder joints to check or anything? There's no hospitals around here, only my workbench and soldering iron downstairs...
Click to expand...

And I say really?? Hey, man, I can understand wanting some help but I don't think anybody here has the service manual for the 488 memorized or anything...not sure if anybody here even has the service manual. There are quite possibly thousands of solder joints in the 488.

So that aside, its not the heads. The 488, along with all the multitrack cassette machines produced by Teac/Tascam were two-head machines so if it is reproducing fine then it should also record fine as far as the head is concerned.

Because the problem manifests for both tracks 2 and 6 I would first suspect something in between the record amp and the track routing switch. If it was something specific to ONLY one track then I'd look post routing switch.

I'm not surprised that the meter shows fine because that will be driven by a separate amplifier. If you had a schematic that would help you narrow down the fault as being post meter amp circuit but pre track routing switch, but without the schematic that would be a bit of an exercise to track down just where that junction occurs in the guts.

Because of your description of the problem (i.e. gross crackly on loud peaks but nothing else gets through) I'd direct you toward a blown opamp, and or possibly a bad cap.

I don't even know what kind of opamps are in the 488mkII.

So unless somebody has the service manual I can't help you any further, but I'd be surprised if it was a bad solder joint. Likely somebody at some point blasted something into an input and an opamp went into overdrive, or a cap aged out and failed.

You may be able to test the whole solder joint thing or possible oxidized connector by opening it up and, while powered and recording to tracks 2 or 6 exercise internal cable connections and/or gently apply pressure to different points of whatever you can identify as the record/reproduce amp card in there. Never had one of those apart...had my 424mkII opened up awhile ago but there again I was dealing with another issue and didn't pay attention to the PCB's, which would be different in yours anyway.

If it was me: I'd find the PCB upon which the track routing switches are mounted, trace the 2/6 switch back to its source which, at some point, would be the record amp circuit and look for an opamp or two and some caps and start shotgunning.

Actually...the VERY first thing I would do is track down a service manual.
 
Thanks, Sweetbeats! That was the reply I was hoping for. I'll find a free night, and call my buddy over... And work on finding a service manual.
 
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