Issue 2 Oric-1 Repair

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Vyper68
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Issue 2 Oric-1 Repair

Post by Vyper68 »

Hi,
Does anyone have any experience working on issue 2 boards? I have been given one to fix and I have it down to the RAM as the ULA, CPU, VIA and ROM are all good.
The Address lines are all present and the MA lines to the LS257’s are there too, from there on it’s a bit confusing. Some of the Address lines from the LS257’s do not go to to the correct PIN number on the 4164’s.
Before I remove the RAM again and take all the new sockets off I fitted is there any reason this would happen on the issue 2 board. I am using the newest schematic so I was wondering if the layout is different.
Bazinga!

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Vyper68
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Re: Issue 2 Oric-1 Repair

Post by Vyper68 »

To clarify .. The MA lines come from the ULA to the respective pin on the LS257 as per the schematic but the line out from the LS257 to the Address pins on the RAM chips do not go where they should based on the schematic.
For example pin 9 on IC20 should be MA6 which should go to pin 13 goes to pin 5 which is for MA0.
Bazinga!

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mikeb
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Re: Issue 2 Oric-1 Repair

Post by mikeb »

Vyper68 wrote:
Thu Sep 03, 2020 3:44 pm
To clarify .. The MA lines come from the ULA to the respective pin on the LS257 as per the schematic but the line out from the LS257 to the Address pins on the RAM chips do not go where they should based on the schematic.
For example pin 9 on IC20 should be MA6 which should go to pin 13 goes to pin 5 which is for MA0.
On my Issue 3 schematic (as Oric Owner/Adv User Guide), it shows IC20/P9 does go to P5 of all DRAM. Why do you say "should go to pin 13" ? Is this because you're seeing that Oric A0 passes through that multiplexer, but isn't going to "MA0" of the DRAM as per the datasheet for a 4164? If so, no worries!

In my opinion: If all 8 outputs from the multiplexers go to all 8 row/col addresses of the DRAM chips, on a one-to-one basis, then it will work.

They probably changed the order of the pins to make board layout easier. This is a trick that can catch you out, esp. when it's done to an EPROM/ROM, which when read and disassembled will have nonsense contents. It can happen to a databus too. Both at once is nasty! (Primitive copy protection).

For DRAM, if it gets scrambled going in, it gets unscrambled coming out. For ROM/EPROM, you have to take hardware/software actions to scramble the data on programming so it will unscramble in use. For clarity, it's best avoided ;)

By my eye the "correct" mapping in Oric is :-

Code: Select all

CPU---DRAM
A0    13 (A6)
A1    12 (A3)
A2    11 (A4)
A3    10 (A5)
A4    7 (A1)
A5    6 (A2)
A6    5 (A0)
A7    9 (A7)

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Vyper68
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Re: Issue 2 Oric-1 Repair

Post by Vyper68 »

Hi Mike
I am not sure currently but the MA Lines from the ULA and Address Lines from the ROM all follow the schematic I have but on the "other" side of the 74LS257's going to the RAM I get the following...
I think I am going to have to take the sockets off and check the tracks. I clipped the old RAM out to minimise damage to the PCB but somethings not right. Although it seems to be back to where it was when I found it although now the Speaker seems to have died now there was noise/static when it arrived but now it is totally silent.
The schematic shows MA0 as arriving on Pin 5 ( A0 ) on the RAM and MA1 as arriving at A1 which is Pin 7 and so on following the Pinout for a 4164 RAM chip. That was how I was looking at the RAM.

Code: Select all

74LS257 ----------------- RAM

IC20 Pin 9   ( MA6 )       Pin 5   ( A0 )
IC20 Pin 12 ( MA7 )       Pin 9   ( A7 )
IC20 Pin 7   ( MA2 )       Pin 6   ( A2 )
IC20 Pin 4   ( MA3 )       Pin 10 ( A5 )

IC8 Pin 9    ( MA5 )        Pin 11 & Pin 13 ( A4 & A6 )
IC8 Pin 12  ( MA4 )        Pin 7 ( A1 )
IC8 Pin 7    ( MA0 )        Pin 11 & Pin 13 ( A4 & A6 )
IC8 Pin 4    ( MA1 )        Pin 12 ( A3 )
Bazinga!

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mikeb
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Re: Issue 2 Oric-1 Repair

Post by mikeb »

Vyper68 wrote:
Thu Sep 03, 2020 5:13 pm

That was how I was looking at the RAM.

Code: Select all

74LS257 ----------------- RAM

IC20 Pin 9   ( MA6 )       Pin 5   ( A0 )
IC20 Pin 12 ( MA7 )       Pin 9   ( A7 )
IC20 Pin 7   ( MA2 )       Pin 6   ( A2 )
IC20 Pin 4   ( MA3 )       Pin 10 ( A5 )

IC8 Pin 9    ( MA5 )        Pin 11 & Pin 13 ( A4 & A6 )
IC8 Pin 12  ( MA4 )        Pin 7 ( A1 )
IC8 Pin 7    ( MA0 )        Pin 11 & Pin 13 ( A4 & A6 )
IC8 Pin 4    ( MA1 )        Pin 12 ( A3 )
I don't understand how MA5 can go to pin 11 and pin 13 (A4, A6) when MA0 also does that. Looks like you have a short between MA5 or MA0.

If that's what you're measuring: it's wrong. It's certainly not aligned with the schematic (or common sense ;) ...

Again, as long as ONE address line from A0-A7 (CPU) is multiplexed with 1 address line from the ULA (A8-A15, or other ULA doings!) into 1 row-col address going to each of the 8 DRAM chips, that's good. The order doesn't matter (although it does look like your order is at odds with an Issue 3 board/schematic but that shouldn't stop things working).

A short between Pin 11/13 of the DRAM would spoil things!

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Re: Issue 2 Oric-1 Repair

Post by Vyper68 »

Yes 11 and 13 were shorted by a tiny bit of solder across two tracks where the solder mask was missing :oops:

The PCB is definitely laid out differently as some of the service mods like putting a 220Ohm resistor on pin 2 of IC21 the place where you cut doesn’t exist. The track is on the top and goes under one of the PAL/RF logic IC’s and the some via’s to Pin 7 of the ULA. So I have done the AY mod and will refit the 1K & 2.2uf parts to the 6522A and leave it at that. It had service bulletin 52 done with some Kynar wire swapping pins 19 & 21 of the ULA around and some Kynar wire linking Pin 1 on both EPROM’s to the 5v rail.
Bazinga!

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Re: Issue 2 Oric-1 Repair

Post by mikeb »

Vyper68 wrote:
Fri Sep 04, 2020 2:36 pm
Yes 11 and 13 were shorted by a tiny bit of solder across two tracks where the solder mask was missing :oops:
Ah, it happens! At least it wasn't between the 12v/0v rail on a DIY plugin board in a PC (Switch on, flash, bang!) ...

Don't leave us dangling, does it work now? :)

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Re: Issue 2 Oric-1 Repair

Post by Vyper68 »

Yeah!
The Oric-1 lives BUT the loudspeaker is not working. I replaced the LM386 and 220uf capacitor so that’s not the problem. I thought it had let go when I couldn’t even hear the normal Oric background “noise” when plugged and sat idle.
Anyone have a spare or know of a source of spares or failing that a modern workaround.
Bazinga!

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Vyper68
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Re: Issue 2 Oric-1 Repair

Post by Vyper68 »

Fixed the loudspeaker now ( dry solder joint ) so we have a working Oric-1 issue 2 :D
Bazinga!

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Re: Issue 2 Oric-1 Repair

Post by mikeb »

Vyper68 wrote:
Fri Sep 04, 2020 6:43 pm
Fixed the loudspeaker now ( dry solder joint ) so we have a working Oric-1 issue 2 :D
Yay! Why is there no "Happy Dance" smiley?

One of the Orics here has a non-original speaker, as the original blew up (too many hours trying to play Damsel In Distress on high volume!)

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Re: Issue 2 Oric-1 Repair

Post by Vyper68 »

Hey Mike have you ever had any experience troubleshooting the 3” drive in a Microdisc ( Hitachi HFD-305SE ) before? I have one here that spins up but in all other respects seems unresponsive. The logic board is sound as it works with my Gotek drive.
Bazinga!

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Re: Issue 2 Oric-1 Repair

Post by mikeb »

Vyper68 wrote:
Sat Sep 05, 2020 10:02 pm
Hey Mike have you ever had any experience troubleshooting the 3” drive in a Microdisc ( Hitachi HFD-305SE )
Sadly no -- I don't think I've ever USED a 3" drive :)

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Re: Issue 2 Oric-1 Repair

Post by iss »

Vyper68 wrote:
Sat Sep 05, 2020 10:02 pm
... the 3” drive in a Microdisc ( Hitachi HFD-305SE )...
@Vyper68: Are you sure that the drive's model is exactly HFD305SE? Because HFD305SE is intended for Apple][ :shock: and there are lot of things which make it incompatible with Microdisc - rotation speed, data encoding, etc... Maybe the only common thing is the last one of the "Handling Precautions": ;)
hp.png
But if the model is HFD305S then we can think about a way to fix it... starting with the jumper for Drive Selection :).

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Re: Issue 2 Oric-1 Repair

Post by Vyper68 »

Yeah my bad it’s a HFD-305S from a Microdisc and I had found a manual for the 305 and the Jumpers are set correctly. So I think I need to get my magnifying glass and check. The Microdisc is a friends and it was working for a short while and then started to have formatting problems then read and write issues and then stopped working altogether. So It was a gradual failure rather than a sudden breakdown.
Bazinga!

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Re: Issue 2 Oric-1 Repair

Post by Chema »

I am sure you already checked, but just in case, could it be just a defective drive belt?

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