Spectrum 128 +2a repair log

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May 222012
 

As Ive been doing some repairs on divIDE’s and I didn’t already own one, I picked up a nice cheap 128 on eBay the other day, sold as powering up but wont load games.
At first I suspected it was just a dodgy tape drive and as I would be using the divIDE to load stuff it didn’t bother me.

So, it arrived and I powered it up and it worked OK. I loaded up my test game and it loaded fine but then crashed. I tried it again a few more times but kept crashing at random points. Time for another going over with the 9010 I thought, only when I fitted it, it no longer crashed. I replaced the Z80 for a brand new one and its been fine.

Nice and easy

 Posted by at 6:22 pm

Spectrum divIDE repair log #1

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May 202012
 

The divIDE, as the name suggests, allows IDE devices to be used on a Spectrum computer.
Got 2 of these to fix recently.

Both of them would not allow the Spectrum(s) to boot up. When I tried, I got to the boot up screen but it was locked up.
As all the chips are socketed I checked them first.

I started with the green PCB.
I found was a blank EEPROM which I reprogrammed with the FATWare bios.

On fixing all the initial faults neither board would work still.
To try and make some short work of fault finding I removed the Z80 processor and fitted the Fluke 9010.
With this fitted I basically ran a loop test on each address and data line and the status lines.

Found that data line 3 was not making it back from the EEPROM to the processor. Following the traces back I found the pin at the edge connector had come away from the solder pad.

I re soldered and tested. The divIDE was fully working again.

On to the red PCB
All the GAL chips could not be read out at all and flagged up errors on pins. The RAM also failed when I tested it.
Talking to Questor on the RCM forums, he tells me that dead GAL chips are a sign of the device being removed while the unit is still powered up.
After some quick probing around I found a transistor had blown. I also took a gamble and tested the other 2, both of which were dead.
After replacing all of these, this unit is now working too.


A nice device but would benefit from a case I think.

 Posted by at 11:16 am
Feb 252012
 

Motherboard clearly had a dodgy ON/OFF switch.
Removed it and replaced it with one from a C64.

On power up I had a blank screen.
Did a few quick checks with the scope and all data/address lines were pulsing properly.
Checked the voltages with a multimeter, the 5v was present but the 9VAC was not. Traced this right the way back to the switch I had fitted.
When I soldered the new switch in, one of the legs musnt have made a connection as they were a little shorter than the original. I resoldered the legs on top of the motherboard as well as the underside and it now boots up.

One of the CIA chips was missing, fitted a new one and C64 mode now works too.

 Posted by at 4:26 pm

VIC20 repair log

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Jan 072012
 

Got Stiggys other VIC20 the other day, it wont load anything via the serial port and just reports back “DEVICE NOT PRESENT”.
According to Ray Carlsen this can be caused by a dodgy 7406 IC and he wasn’t wrong.

I checked all the states of this chip with a logic probe and all seemed to be as it should be so I went through each gate with a logic pulser and checked for its output. The outputs on pins 4 and 6 were stuck.

Removed the chip and eventually found one on a C64c motherboard that was scrap.
Replaced and tested with a demo and a couple of games.

I also took this opportunity to try out the VIC20 JiffyDOS (PAL).
My original test with JiffyDOS on this failed, nothing would load up. Turns out there is an NTSC and a PAL version, the later being significantly harder to find but we got there in the end.

 Posted by at 5:18 pm

Amiga 4000 repair log

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Dec 012011
 

Its been a good week for repairs this week. Got Jimbob’s Amiga 4000 here which would constantly reset with any RAM in bank 0 and would not detect any RAM at all with bank 0 empty.

The board has had some repair work done before but its been done to an excellent standard. The new SIMM sockets looked flawless so that was my first suspicion down the pan. I checked the on board battery which was showing the first signs of “furring” on the contact. The battery was completely dead so I replaced this while I had the board out. There doesn’t look like there has been any battery leakage but I cleaned up the area anyway just in case.

With a bit of internet searching and a bit of probing I found a knackered 74F245 transceiver at location U891. I ordered some up and replaced it.

Fired up the unit and checked the free RAM

Played a game of Blood Money for good measure.

 Posted by at 5:07 pm