Portastudio 688 or 244

[Daryl johns]

Hey guys, I've had a tascam 644 and it broke. I was about to get the 688 , but then I heard a recording from it that sounded so clean. Now I'm into Mac demarcos "Rock n roll nightclub" album that he recorded on a 244. Although its limited to 4 tracks, I feel like since its older it has a trumpeter cool fucked up tape sound wheas the 688 sounds cleaner from the video I headd. My 644 had a cool vibe, but was wondering u had any thoughts about maintaining that sound I want over the convenience of the 8 tracks. Thanks!! Mabye I could record into the cassette and dump the tracks the computer . I sol any me music to sound tapy and cool but I'd also like the 8 tracks, idk Mabye I'm wrong about the 688

 

[Daryl johns]

Didn't mean to say tumpeter

 

[jreitz]

Would you sell the power supply to the 644 I lost mine.
Thanks john

 

[SkywaveTDR]

The 244 can be maintained easier and less costly than the higher up and more complex models.
I am sure that I have worked on 100 by now.
Power supply wise I just made a supply for a 424 unit- it is all determining what was in the original one and making something better and something that can be repaired if needed.

 

[John Mackenzie]

I totally loved my 688, and still do, but trying to get it repaired at the moment. Nice to use, very versatile with Midi sync and also as a live band mixing desk (+ recording at the same time) . if you can afford it, I highly recommend this unit for nice analogue sounds.

 

[SkywaveTDR]

Where are you getting it repaired?

 

[John Mackenzie]

Hi Skywave. I am going to try and repair this myself, once I get service manual from USA. I am in Scotland, with very few repair shops now. I have found a damaged Chip inside the unit, but worried that something else may have caused it to blow . There is one shop in Edinburgh who specialise in "retro" gear, tape decks in particular. I might just take it to them to gt it done properly. Retroreproduction is the name. a couple of pics to let you see what I am up against !!

 

[SkywaveTDR]

Hi John,
You have it easy as not all chip yell out at you about their demise. Put a socket in and change the chip, if it blows out then figure what is going on before the next one. Check power supplies first. That is a catastrophic failure of a chip. It is possible that an input source caused this as a lot of inputs are connected that should not go into this device. Report back when you can.

 

[John Mackenzie]

Hello Skywave. Thank you for your interest in this repair. I realise that you are also in communication with Rohmal about this. It is so good to have experts advice . I am very grateful. Just to be clear about a few things : my 688 does power up, tape mechanism works fine, after replacing capstan belt. All other functions, like Scene memory etc. battery, and all other functions work as normal. Just no audio signals getting through, either from Inputs or from tape. I can hear a low level 50Hz hum when I listen on headphones, This hum is affected by master volume/monitor control, so some signal is getting through to output amp. I am going to do exactly s you have suggested, replace the IC CD4066B, (after fitting a DIL 14 pin socket), and give it a try. I am waiting for the parts to be delivered, probably today. I will check power supply voltages before doing this. None of my fuses have blown, which is perhaps a good sign ? The power supply in this machine is internal, with only a 250V connector going in to the unit. I can easily check transformer and diodes/ capacitors for voltage outputs before I start. I will then check voltages etc at the DIL socket, before inserting the new chip. I do have 5 IC's ordered, as that is the only way they are supplied, so I will have some more to use if the first replacement blows up ! I will keep you informed of progress.

John Mackenzie

 

[SkywaveTDR]

There are cases where musicians take a amplifier output and go down the line blowing out one input after another. I trust this is not how you have the unit. Usually it is very unlikely to have a bunch of circuits go out at once. It is against probability and statistics. However if you get one of these genius people with the 500watt amp plugging into 1/4" plus just because they fit- it is possible to get a piece in that is all blown out. Assuming from what you tell me so far that this is not done, then one can assume that the power supply either is defective or is not getting to the audio board. When you see Op Amps such as NJM4558 or any 4558 op amp you can find if the rails are there by just measuring voltage on pin 8 (plus rail) and then pin 4 which can be the negative rail or even ground in a case that a bipolar supply is not used. Most likely in your case there will be plus/Minus 12Vdc or around that.
I have replaced more CD4066 IC's than I can remember- probably hundreds of them. They are not the most reliable part that can be used but the cheapest. They are very easily damaged by static or voltage spikes.

 

[John Mackenzie]

Than you again Skywave. You give me hope that I can find the fault. In my previous employment I did have signal generator and oscilloscope to trace faults, but I do not have these at home. I only have a good multimeter to make simple measurements. I shall investigate some more on the power/voltage side of things around the various components. My new CD4066 IC is fitted, and "looks "intact after powering up, but still no audio signals on inputs or tape outputs. The faint hum that I can hear does respond to the master volume control, which suggests something is still functional in the output stages.

 

[rohmal]

Dear John, What happened to the 688 You were supposed to get. If you get it You can easily interchange the boards and see if it's OK. See about it so you can reach the shores early.

 

[SkywaveTDR]

Changing boards is an amateurs way to do things and you waste a lot of time that otherwise could be used to fix the product. It is like the question I get all the time about a unit having trouble because of a fuse. The fuse solution of the equipment went out with the 60's. Hardly any equipment will have any problems related to a fuse. The fuse blowing out is a symptom of the problem not the cause.
If you research what is wrong with the unit you will find a bad cap or op amp that will be sucked out and replaced faster than moving a different board around.

 

[wkrbee]

Just a FYI.The 4066 ICs are running at their Max.recommended voltage.The better replacement is the 4966 which has a higher Max recommended voltage.The meters peaking and dropping back on power up is a clear sign you have DC on the audio path-which is typically the failure mode of the 4066-the control voltage shorts to the I/O.

 

[rohmal]

Dear my Senior Sam I agree with what You said about changing the boards of 688. I suggested it as I thought it was easier for John than tracing the signal path which he is not used to. I just wanted him to follow the easy way for him. Sorry if I have gone against your solid rules of trouble shooting. Pardon me for that. Wish you will give John the required help in due course. Wish You a good day.

 

[John Mackenzie]

Just a FYI.The 4066 ICs are running at their Max.recommended voltage.The better replacement is the 4966 which has a higher Max recommended voltage.The meters peaking and dropping back on power up is a clear sign you have DC on the audio path-which is typically the failure mode of the 4066-the control voltage shorts to the I/O.

This is superb information. Thank you wkrbee . I shall use this in my attempt to fix.

 

[ctreitzell]

What happened? Mr Mackenzie, did you succeed?