Tandy 1400FD Power Supply Capacitors

[jmetal88]

I've developed a renewed interest in getting my Tandy 1400FD running again, but I have a little bit of a problem: Apparently the last time I was working on it, I took off a bunch of leaking capacitors off the power supply and either didn't write down what they were supposed to be or lost the piece of paper I was making notes on. Either way I need to know the values of the electrolytic capacitors on the power supply and I'm hoping someone here can help me out. So if anyone has a 1400FD they wouldn't mind taking apart (or maybe even the 1400HD would help? I'm not sure if they use the same supply or not, but I did find an old post from someone saying they put the power supply from one into the other once) to read me the values of the electrolytic capacitors on the board, I'd really appreciate it. I'd really like the full list, but if that's too much trouble there are a handful of capacitors that I think may be critical values: C51, C52, C43, C45, C34, C4, and C15. I'd also appreciate pictures of the board -- I had a couple of other components I took off that I had hanging around loose with the board and pictures would help me verify that I put the right components back on.


And before someone mentions it, I'm aware that there's a 1400LT service manual posted somewhere, but I've looked at it already and the power supply schematic in there is significantly different from what's on my board so it doesn't really help.

 

[jmetal88]

No help yet, huh?

I just e-mailed Radio Shack to see if they might still have a copy of the service manual anywhere, but I'm not really holding out hope on that, haha.

 

[jmetal88]

As expected, Radio Shack wasn't of any help.

I would also consider buying another broken 1400FD off somebody here, provided the insides haven't been messed with, so I can look at the power supply board myself.

 

[jmetal88]

I guess I'm too impatient -- I started putting offers up on eBay and now I'm going to be getting an untested/potentially broken 1400LT. Not an FD, but similar specs and at least with the service manual for this one out there, I'll have a better chance at getting it running if it does turn out to be broken.

I am not sure what I'll do with my 1400FD now, though.

 

[jmetal88]

I got the 1400LT and of course it works fine. xD

It did have one small problem in that it initially would not turn off -- it stayed powered up no matter what position the switch was in. I believe the cause of the issue was electrolyte from a capacitor that had leaked in the power supply. It looked like it had pooled up around a couple of resistors involved in controlling the main power transistor, resulting in the transistor being switched on all the time regardless of the actual power switch position. I say "I think" because the symptom got better after cleaning the PCB, but I had also re-soldered a couple of components before then as well (the electrolyte seems like the most likely cause of that transistor staying powered up, though).

As I suspected, none of the PCBs from the 1400FD are interchangeable with the 1400LT, so I guess now I have a bunch of 1400FD parts in unknown condition that I don't know what to do with.

 

[docangle]

I got the 1400LT and of course it works fine. xD

It did have one small problem in that it initially would not turn off -- it stayed powered up no matter what position the switch was in. I believe the cause of the issue was electrolyte from a capacitor that had leaked in the power supply. It looked like it had pooled up around a couple of resistors involved in controlling the main power transistor, resulting in the transistor being switched on all the time regardless of the actual power switch position. I say "I think" because the symptom got better after cleaning the PCB, but I had also re-soldered a couple of components before then as well (the electrolyte seems like the most likely cause of that transistor staying powered up, though).

As I suspected, none of the PCBs from the 1400FD are interchangeable with the 1400LT, so I guess now I have a bunch of 1400FD parts in unknown condition that I don't know what to do with.

I just picked up one of these machines and it is doing the same thing, the power switch doesn't power off the machine. Also, the startup is hit and-miss, I have to unplug and replug in the machine. I assume it is a capacitor issue. Did you change out the capacitors, I wonder if anyone has a capacitor list for the power supply.

 

[docangle]

Just a follow-up for GP, I received all the replacement capacitors and removed the old ones, some of them were in terrible shape! Especially the large ones, cleaned off the electrolytic fluid with alcohol and inspected the board for bad traces (none found). I installed the new capacitors and everything is working just fine. The first time I turned off the machine and turned it back on, it had a strange behavior with the screen, but after that, it was fine, probably just the capacitors forming. I am waiting for Kevin from Texalec to send me the Custom XT-IDE for this machine, and this project will be complete.