Cap Kit for D32/D64

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unumlapis
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Cap Kit for D32/D64

Post by unumlapis »

Would anyone know whether there are ready capacitor kit for sale for the Dragon 32/64? Or if any one would be able to share a list of the capacitor and other components which would be worth replacing. Plan to do some refurbishing and want it to as much and as well as possible without any shortcuts. So open for some quick advice on the component side.
Last edited by unumlapis on Wed May 22, 2019 9:35 pm, edited 1 time in total.
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unumlapis
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Re: Cap Kit for D32/D64

Post by unumlapis »

So, I'm looking at starting to re-cap a Dragon 32 and 64 and here is what I found of capacitors which I plan to replace. The RF-modul does have one 16v capacitor which I hasn't managed to identify. Also, on the D32 motherboard I'm not 100% sure about C22 since it wasn't really possible to see the values but based on the schematics I believe it's a 100uF 25v. If anyone would be able verify that the below list including filling in the gap for the RF-mod that would be great! Also, any additional suggestions for components to replace is highly appreciated.

D32 PSU-board (Issue 4)
REG2 LM7812 CT
REG3 LM7905 C
C5 220uF 35v
C6 4700uF 16v
C9 4700uF 16v
C8 470uF 35v

D32 RF-mod
C? ?uF 16v

D32 Motherboard (Issue 6)
C13 10uF 25v
C22 100uF 25v
C23 33uF 25v
C35 10uF 25v
C36 100uF 25v
C42 10uF 25v

And then for the Dragon 64:

D64 PSU-board (Issue 4)
REG1 LM309K
REG2 LM1183
REG3 LM7912
C5 220uF 35v
C6 4700uF 16v
C8 470uF 35v
C9 4700uF 16v

D64 RF-mod
C? ?uF 16v

D64 Motherboard (Issue 2A)
C19 10uF 16v
C23 10uF 16vr
C26 100uF 16v
C55 33uF 16v
C63 100uF 16v

And beside the above VR1 potentiometer had heavy oxidation so better replace that one as well but haven't found it in the schematic yet as the quality isn't the best:
Dragon64_VR1_oxide_small.png
Dragon64_VR1_oxide_small.png (172.48 KiB) Viewed 9877 times
Last edited by unumlapis on Thu May 23, 2019 10:42 pm, edited 1 time in total.
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unumlapis
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Re: Cap Kit for D32/D64

Post by unumlapis »

Right then, this is what I'm working with then, one D32 and one D64:
Dragon32-Dragon64.jpg
Dragon32-Dragon64.jpg (251.63 KiB) Viewed 9879 times
Alastair
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Re: Cap Kit for D32/D64

Post by Alastair »

Unless you can see an obvious physical problem with a capacitor I'm not sure if it is worthwhile replacing them. The following post - Let’s Talk About Capacitor Failure by Blake Patterson - also questions the practice, be sure to read the responses and to check out the links.

A more definite answer would come if we knew if anyone has suffered capacitor problems in their Dragon(s), and if so how many Dragons have had problems. My personal experience is that the last time I switched on my unaltered 1982 vintage Dragon 32, which would have been sometime in 2018, it still worked.

As for VR1, just try cleaning it in the manner described by Stew in another thread.
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unumlapis
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Re: Cap Kit for D32/D64

Post by unumlapis »

Thanks for the links will read and pick up from them. I don't have any referens to any Dragon computers and whether they're better built than other systems and if the would hold up better. But, I'm just ref to discussions with C64 and Amiga owners which directly indicated that replacing all the electrolyte caps would benefit the overall status of the computers. For some the system worked from anything from couple of hours to week or two and then caps started to pop for them. Whether it's a myth well spread within the retro scene I don't know. So I'm currently just looking at it from the view of that it's a cheap and quick replacement which wouldn't make thing worse.
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unumlapis
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Re: Cap Kit for D32/D64

Post by unumlapis »

Alastair wrote: Thu May 23, 2019 11:18 pmA more definite answer would come if we knew if anyone has suffered capacitor problems in their Dragon(s), and if so how many Dragons have had problems. My personal experience is that the last time I switched on my unaltered 1982 vintage Dragon 32, which would have been sometime in 2018, it still worked.
Once again, thanks for good links and I've been reading comments and following additional links and it's clearly seems to be part of the Commodore community to replace caps on old system which might not be necessary. If something should be done, well, then it would be the ensure that the power supply works as it should, guess that this could cause issues and I do know that the newer power supplies which came with the later Amigas was really bad. The newer PS had the same housing but almost no weight. So can assume that this of course causing a lot of grief for many Amiga owners. Then again, with the C64, don't know what there has been such a stress with them.

So for now, I'm going to hold back on re-cap on the Dragons and just taking a swing on the PSU boards and ensuring that the power supplies in sounds order or just build some new ones as it's quickly done.
Alastair
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Re: Cap Kit for D32/D64

Post by Alastair »

Thanks should really go to the CoCo Crew Podcast as it was their most recent podcast that brought Blake Patterson's article to my attention.
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unumlapis
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Re: Cap Kit for D32/D64

Post by unumlapis »

Next up was to check the original power supply that came along with the Dragon 64 since this was missing from the Dragon 32. Before checking checking the power output I verified that I could measure resistant on the three different windings to confirm that the power supply wasn't a burner. Below is what I expected to get:

Pin/Function:
1 8.5V VAC
2 8.5V VAC
3 28V VAC
4 0V (centre-tap)
5 28V VAC
6 Connected to pin 1 inside PSU plug
7 Connected to pin 2 inside PSU plug
8 Not in Use
9 Not in Use

When measuring the different windings based on the above VAC expectations I get 10.8 VAC, 17.7 VAC and 36.0 VAC. So based on the feedback from the D32/D64 owners group on FB it seems to be okej.

Finally then it's time to test the D32/D64 PSU board and I got the following values using the same externa power supply that I have:
d32-d64_PowerBoard_Measurement.PNG
d32-d64_PowerBoard_Measurement.PNG (8.75 KiB) Viewed 9814 times
So both measurement shows a bit on the higher end and since it's similar on both the power supply boards I guess that the original power supply might not be the best.
sorchard
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Re: Cap Kit for D32/D64

Post by sorchard »

Replacing some of the caps on the Dragon main board can be pretty challenging. I don't like doing it even with pro tools. It's made worse by the lack of thermal relief pads, meaning connections to large areas of copper require a lot of heat and/or preheat to get the solder to melt. Too much heat of course comes with the risk of losing the solder pads and destroying the through-hole plating.

That said, one or two of the tantalum bead capacitors near the power connector on the main board can fail on power up after years of storage. This is a weakness of old tantalum caps and I've had it happen on two of my Dragons on first power up after 10-15 years in storage. The dielectric degrades over time if unused. We threw out a drawer full of old unused caps at work as they had a 50% fail rate. If the tantalum caps survive the initial power cycle then they will usually self-heal and recover with use.

Where I have replaced caps, and encountered problems in removing them, I've usually just played it safe and cut the legs, soldering the new cap to the legs of the old cap.

Regarding the measured voltages, it seems strange that two different machines consistently read 20% high on all voltages. It seems far more likely that the DMM is out. I know my one reads high when the battery is getting low.

I've seen some 5V regulators output 6V when unloaded, but I just checked one of my D32s and the PSU board gives -5.2V / +5.0V / +12.0V even when unloaded.

Anything more than 5% out is beyond the recommended operating range of many ICs so it is well worth double checking with another known good DMM.
Stew
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unumlapis
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Re: Cap Kit for D32/D64

Post by unumlapis »

Definity issue with the external power supply based on that did recheck the measurements this morning on the power supply board and now I've lost +5VAC and when checking the expected 12VAC I get 15VAC. Then checked pin 1 and 2 from the power supply directly and it shows nothing. So need to get new power supply. So going to order parts to build two new externa power supplies for both system.
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