Repairing a 8050 for my Vic

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Kakemoms
Vic 20 Nerd
Posts: 740
Joined: Sun Feb 15, 2015 8:45 am

Repairing a 8050 for my Vic

Post by Kakemoms »

Hi

I have started on the task of repairing my 8050 dual diskdrive for my Vic-20. The unit was flashing the front lamp around 4 times which apparently is not used. So I recon it either flashed it 3 times or 5 times (it goes between red and green with a long green ligth, so I am not sure if its the red or green state that is "flashing on"). Anyway I replaced Both HIGH/LOW ROM which resulted in a long red light. Then replaced both 6502s with no change. Then I went on to measure the voltages and found that the 5V was missing... very strange as it "worked" when I started. Well, pushing things on the board sometimes results in cracks, so I thought that might be the case. So I started looking into the power circuit.

Apparently the power supply (disconnected) is supposed to give 16V and 8V AC on different pins, but I either get 0V or 10V, so something is wrong there.

Edit: I found a poor connection and got 9V and 18V AC which are within specifications. It gave a good steady 12V and 5V in the unit. Still, it only shows a red led when switching on, so I replaced the K4 ROM as well (a 2K 2316 which I replaced with a 2564 (filled with 4 copies)). The pin layout is compatible if you don't use pin 1,2 and 27,28.
Next step was to do some logic testing and there is clk2 on both 6502, and their data&address buses are actively running. Strange! It mostly looks like the unit is booting as normal, but there is no led flash codes. So at some stage it stops, or the circuit controlling the led is not working? Hopefully its not the RIOT.
Kakemoms
Vic 20 Nerd
Posts: 740
Joined: Sun Feb 15, 2015 8:45 am

Re: Repairing a 8050 for my Vic

Post by Kakemoms »

Oh... I haven't updated this here.

Its not very Vic-20 related, and I got many great hints on 6502.org, so you can follow the repair there if you want:
http://forum.6502.org/viewtopic.php?f=3 ... 322#p48322
Forbidden64
Vic 20 Hobbyist
Posts: 146
Joined: Sun Feb 28, 2016 9:59 pm
Location: CA USA

Re: Repairing a 8050 for my Vic

Post by Forbidden64 »

It kind of is...if you have the IEEE-488 cart :D. I have one of these drives, and it is in deplorable condition. When it shipped, all the parts, board transformer etc. are all loose and wrapped up to prevent the transformer from crushing everything during shipping lol. I'm not even 100% sure that the drive is complete. The outside is however, in perfect condition! I couldn't really afford one, but I had waited so long to find one, that I bought it anyway. I'm sure this, and the other thread on 6502 will come in handy when I get a computer space again. I was hoping to get a 4040. The seller stated this, and sent an 8050 instead, and in very bad shape. I called it a blessing because it has double the capacity anyway. I can do tape transfers, or get one of those neat little drive emulators for file transfer.

I'll probably have to find mounts/standoffs etc. too, since they are missing.
Kakemoms
Vic 20 Nerd
Posts: 740
Joined: Sun Feb 15, 2015 8:45 am

Re: Repairing a 8050 for my Vic

Post by Kakemoms »

Well, many of the drives of that age isn't working very well, but my 8050 has to have had some kind of record..

My 2040 was crushed but amazingly enough the PCB was still working. I managed to get some apple drives and replaced them, so the unit seems to be working.

I have an original Vic-1112 IEEE-488 cart, a 8296 (PET) and trying to build a CBM B720 (I have most parts, only need time to do it properly).

So.. enough to do?
Kakemoms
Vic 20 Nerd
Posts: 740
Joined: Sun Feb 15, 2015 8:45 am

Re: Repairing a 8050 for my Vic

Post by Kakemoms »

Summary for now:

UL1&UH1 ROMS replaced, 6532's replaced, 6502's replaced, two MM2114 (RAM) replaced, som logic ICs replaced.

Waiting for CAPS. My chinese order got lost in the mail, so had to order new ones. The 220uF cap is down (to 140uF) and I will replace all 10uF, 1uF and the 47uF CAPS (not all were bad, but I want to replace them all).

I also found that the 0.1uF cap at C42 was floating.. it was not connected to 5V on one end. There is no trace on the board, so apparently a design fault. Hopefully its not a polar cap because its mounted the other way compared to C43,44,45.. :shock: (it should be ceramic, so no worry)
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