Tascam 488 plays but does not stop - three LEDs blinking

[Ray Fite]

Hello I just changed the belt of a non-working Tascam 488. Same time i decided to exchange
some switches (play, stop, rewind didn't work) I soldered this while the unit was open. After closing the unit,
you can play a cassette you can hear it playing on headphones...you can even record - but if you press the stop-button the unit does not stop. If you press "stop" - for some time it does nothing (it still plays) and after a second it switches to fast foreward and the three LEDs (green for play, red for record und yellow for pause) are blinking. If you press stop now again it does stop.

Fastforeward and Fastrewind does work. But you cant stop this too. Stop Button does not work. (But its a new switch und you can see that the contact is given)
At the end of the tape the auto-stop funktion does not work ( you see the LEDs blinking again) the unit doesnt stop.
If you use the RTZ-Function (Return to Zero) it does start to rewind but reaching the counter "000" it does not stop but the three LEDs are blinking again.

I did google search but don't find any hint. In the meantime i did exchange all the control-buttons (cause it seems there was a liquid poured over it. Maybe i did something wrong with the exchange ( to much heat while soldering)?

Another problem is the Input 1 Channel - This channel does not record.

If someone knows about that malfunction i'd be happy to hear what to check. The rest of the unit is in great condition The unit does not seem to be used very often.

Greetings
Ray

 

[SkywaveTDR]

Hi Ray,
Many things are hard to figure out from a distance and you are having an issue that we never see so far. But consider this- the stop button probably gets used more than any other button on the deck and they are nothing but tactile switches. I would want to ohm out that switch and see if it is actually working first. I have had to change tact switches here and even in broadcast decks when I was Chief at some Radio Stations. They have the switches at DigiKey where I buy them in the hundreds because like all parts they just love to stop making then after a while. I would not buy 300-400 tact switches if I did not have to change so many on all Porta Studios of this type. The reset and some record enable switches often are intermittent at times. I write down all the bad ones get that board off and then change them .
The other thing that could be the issue is solder joints at connectors. When these are pulled on and that they are really weak non- aerospace grade solder jobs so I often times have to go in and resolder with care these connectors. I do then all if I am to take a board off and my solder joint will not break like the wave solder ones do. I use Kester 44 solder , head magnifiers and a Weller WES51 solder station with a fine conical tip.

 

[Ray Fite]

Thanx for your reply - But i did exchange the Stop-Switch (I exchanged all switches with new ones) - the connectors is a good idea - i will check them with a
permeability checker. But I really think it is something different cause the tape does not stop at the end too. And the issue that the return-to-zero function does not work either, shows me thats no problem of the switches. But connectors could be... I will check these this afternoon....
Greetings Ray

 

[Ray Fite]

I just checked again. You press the "play" button the green LEDs is on. After pressing the "stop" Button - the green LED is then off. After a second all three LEDs are blinking and the maschine is not stopping but switching to fast foreward. If you press STOP then ist really stops.
So it is not the switch of the STOP- Button

 

[SkywaveTDR]

The 488 is a cam operated deck and this being a unit that uses a feedback contact panel, I would say the three LED's are telling you the mechanism controller indicates an error with the LEDs. I would first take off the PCB clean with denatured alcohol as well as contacts on the cam gear and then apply a thin layer of Lubriplate 105 to the PCB and reassemble. IF the mechanism is gummed up with old grease then that would have to be addressed. Doing partial repair work on these older deck get different amounts of crazy results but the cause is the mechanism is gummed up with old grease or the feedback sensor (contact) plate is not getting correct data to feed back to controller.
This feedback PCB is to the rear or above the cam gear that moves the heads and Pinch rollers.

 

[Ray Fite]

I finaly solved the problem. One of these connectors that connect the upper "control PCB" to the one below had some broken solder joints. So just some soldering at that place ( look at the first photo) did solve the problem....Now it works fine - just the first input channel doesnt seeem to work - but i think that problem i will solve soon too. Thanx for your contribution - Finally that was your tip to control the connectors....
Greetings Ray

 

[SkywaveTDR]

Broken solder joints are a regular thing on these but the yellow glue on those capacitors should be taken off as it eats component leads and can be conductive in humidity- we know to take that stuff off the boards now.

 

[Ray Fite]

Maybe you can help me with the channel 1 that does not record properly too?
I found out that the channel 1 is not totaly dead. If you switch the input-volume-poti to the left! you can hear a small input signal. Not much volume (just one or two LEDs on the meter) But if you turn up the input-poti to the right instead of getting a louder signal, the signal is disappearing.
Any idea what to check?

 

[Ray Fite]

My Input-Channel one still does not work right.
Input Channel is low when poti turned to the left, I exchanged the resistance R101. It had 140 kOhm instead of 100 Ohm. Now you can use the Channel 1 as input channel but still not for Microphone inputs. I think one channel of the NEC c4570HA Chip ist dead. Today I ordered one in China. Shipping lasts a least 3 weeks. I will report if i know more....
https://datasheetspdf.com/datasheet/C4570HA.html

Greetings
Ray

 

[Ray Fite]

Now i replaced the C4570HA and that was the reason that the Channel1 doesnt work.


https://www.ebay.de/itm/5pcs-UPC457...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

Now my 488 works with stereo micro - all Channels inputs work. Great machine.
Thanx for your help. Greetings Ray

In the picture you see left the old one - right the new one. Now I've got 4 parts in reserve