Tascam 34B do not work at some channel

elsinoacat

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Dec 20, 2016
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Gear owned
34B 22-2 22-4
I have 34B . It has been left untreated many years. I fixed it to move in these days .(By attaching a belt and a pinch roller) The head and the mechanical action are all good.
Output, recording operation check is as follows.
1. channel 1 : output work well,recording can not ,but slightly can overwrite.
2.channel 2 : no sound,no recording,VUmeter never shake input and output.
3.channel 3 : output,input sometimes work well. When output does not work, it gose well
by using cue lever to add high frequency playback signal .
      and If I do the same operation in channel 2 it is valid occasionally.
4.channel 4 :no sound,no recording,VUmeter shake well input and output.
sometime it works well when output ground signal on head is dropped to ground.
But it works well only SYNC mode,never REPRO mode.
I did the following to solve them.
1. I looked for a service manual but there were no 34 but 38
2.I checked all of the contacts of every variabl resistors for calibration.
3.I replaced each amplifier board in a different place.I replaced the new relay on the board of channel 4.
 But the result never changed.

What is the cause? Does anyone have a hint of solution?
 
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self reply

I got such a reference reply from another threads. Is it correct?

http://www.tascamforums.com/threads/tascam-38-head-issues.3400/
wkrbee
Member
wrote
>The 30 series decks 32,34,38,had problems with the soldering on the motherboard >degrading.Your problems are consistent with flaky solder-I fixed a lot of them with this >problem.
 
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I have seen motherboard problems and relay problems and now some capacitor problems on the 30 series decks. There can be different things and you need to figure out what it is.
 
skywaveTDR thanks,reply.
>some capacitor problems on the 30 series decks.

I do re-solder of a motherboard and I determined to exchange a capacitor with your advice.
So
Are those specified by chemical capacitor ?
I don't know whether it's necessary to exchange all those.
I'd like to limit the number for it. Because there are 4 boards which should be handled.
 
Self reply and Result
I succeeded in my making a machine function perfectly today.

I took out the motherboard from the machine and re-sold all the points, as pointed out by other threads.
I did not replace the indicated capacitor. Because it was healthy to see it.
After all it was possible to repair by merely re-soldering the motherboard.

Member wkrbee thanks Your remarks were correct.
 
Looking at Electrolytic capacitors as a sign of failure is really only effective about 30% of the time and maybe less than that. I have perfectly looking Mashushita caps from a Pioneer RT909 that are dead short and look new. Looks are no way to evaluate and changing out 30 years old caps is the smart think to do unless you like working a screw driver many time not to mention the aggravation. The motherboard is often time the problem but can not always be the solution. I had a 2 day fight with a A3440 that had all kinds of things wrong with it. I won though.
 

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