The Mandatory Modifications

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Cristian
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The Mandatory Modifications

Postby Cristian » Wed Oct 25, 2017 10:45 pm

The QL Service Manual describes some "mandatory modifications":
http://www.sinclairql.net/srv/qlsm4.html#s4c
Has anyone applied them (or also other mods described in the manual)? With which results?


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tofro
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Re: The Mandatory Modifications

Postby tofro » Wed Oct 25, 2017 11:03 pm

On one of my QLS (a JS model) this seems to have been done at the factory (did never come around to check if really all the mods were done), or at a pretty good repair site, solder joints in no way look different than the others.

And well, it works. No idea how it would work without the mods, though.

Tobias


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Cristian
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Re: The Mandatory Modifications

Postby Cristian » Thu Oct 26, 2017 1:19 pm

Yes Tobias,
indeed the manual explains that "With build state D12 or higher the modifications [but only the ones described in page 4.3 and page 5.1] have already been incorporated".
The other modifications to do are mainly on the hidden (solder) side of motherboard, so they're difficult to find.
I suppose that most of people didn't "run the risk" and left their QLs as they was.
And also your board tracks seem factory cut?
So, if you can confirm that the modification are applied and you QLs are fully functional, I suppose I may proceed


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Re: The Mandatory Modifications

Postby tcat » Thu Dec 07, 2017 12:55 pm

Hi Cristian,

We went through `Microdrive design' topic together :-). Being no expert, please find my observations.

This is a summary of mandatory modifications.
1. Add resistor R104 (82 Ω) in TR1 collector circuit. It should be noted that this resistor is fitted in a non-standard way in the collector leg
between the transistor and the board.
2. Replace resistor R92 (was 220 Ω) with a resistor of value 390 Ω.
3. Add resistor R105 (1 KΩ) across capacitor C19.
4. Add resistor R106 (1 KΩ) across diode D17.
5. Add diode D22 (1N4148) in series with R100.
6. Add diode D23 (1N4148) in series with R101.
7. Add resistors R102, R103 (33 KΩ) between pins 19 and 21 of IC23 and VM12 (-12V rail). It is convenient to do this by laying the resistors on
top of IC23 and running a flying lead from their common connection to pin 1 (VM12) of IC25.
8. If EPROMs are fitted, upgrade firmware (IC33, IC34) to D11 standard and return salvaged EPROMs to Sinclair Research Limited. Details of
the methods used to upgrade to D11 standard are set out in sub-section 4.
9. Add MDV2 stand-off spacer.


The mod 5,6) we have discussed already, these add extra diodes on MDV head board. They should prevent drive from selecting when having no cartridge inserted. Your Iss#5 drives do not have them applied.

A visual indication whether the mods have been factory applied, is to look for flying resistors on top of ULA. See picture.

ULA-mods.JPG
flying resistors on top of ULA ZX8302

As already discussed, MDV in slot 1, should have screen foil on its ULA, to shield off noise coming from the PAL and TV modulator.

MDV in slot 2, may induce some noise from power-ground on copper side as its ULA is situated right above. The recommended mod is to divert the power-ground away from the ULA. See picture.

MD-mod.JPG
md performance mod on Iss#6 board

MDV in slot 2, may tend to format much fewer sectors, on occasions cannot complete format at all, while outside the slot 2 they can format alright. In such situations the mod can help.

Tomas


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Cristian
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Re: The Mandatory Modifications

Postby Cristian » Sat Dec 09, 2017 12:11 am

Thank you very much Tomas: now it's all clear :)


tcat
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Re: The Mandatory Modifications

Postby tcat » Sat Dec 09, 2017 1:40 pm

Hi Cristian,

Just observations, need to be proved by experience of others.

I reckon you have Iss#5 QL board to service, I wish to learn from your steps, if you shared here in the forum, I may do the same in parallel.

Tomas


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Cristian
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Re: The Mandatory Modifications

Postby Cristian » Sun Dec 10, 2017 7:45 pm

tcat wrote:need to be proved by experience of others.
I wish to learn from your steps

...or from my mistakes, as a "guinea pig" :mrgreen:
Seriously speaking, I'll be happy to share my progress... if any. Unfortunately I'm not exactly a hardware genious



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