Modular clock issue

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10 months 2 weeks ago #12668 by roadrune
Replied by roadrune on topic Modular clock issue
The test points start at 5VDC, but slowly drains and within about 30 seconds it was below 4V, i thought i could measure the 170V test point, but just as i was about to move to it i noticed a smell of something overheating, i powered down and could feel Q1 being seriously hot, i would guess around 100°C.

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10 months 2 weeks ago #12669 by Ty_Eeberfest
Replied by Ty_Eeberfest on topic Modular clock issue
Okay... when the +5V rail deteriorates anything can happen, none of it good, with no real way to predict what will malfunction first. The +5V rail powers almost everything on the board.

The hot MOSFET Q1 could very well be a symptom of the low +5V. If it's still hot after getting +5V sorted we can look at it then.

First of all, take a reading of VIN (voltage coming from PSU) on the board. You can use the VIN pad on P1 (right side of board) and the ground test point that's next to it. We need to be absolutely sure the PSU is not deteriorating / drooping under load before looking elsewhere.

If VIN is stable you have 2, maybe 3 parts that could cause the problem. Follow along on the schematic: First choice is the 33uH inductor (L2) because it looks crusty like it might have gotten hot or something. Second choice is the LM2596T-5 voltage regulator (IC1). It's the only active component in the +5V regulation circuit. Third and unlikely part would be the 1N5819 "smack-back suppressor" diode (D3). If it failed shorted there would probably be no +5V at all, and if it failed open then IC1 would probably be damaged or killed by spikes from the inductor not being suppressed.

I don't have any parts to send you. You'll need to contact Ian through the shop site if you need to get any replacement parts. Or maybe he will turn up here.

Look into it later when the dust is clearing off the crater.

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10 months 2 weeks ago #12670 by roadrune
Replied by roadrune on topic Modular clock issue
VIN is stable at 8.97V for at least ten seconds, i am afraid to run it longer then that, when the tubes flash it dropped to 8.94V.
Q1 was cold after ten seconds.

As for the components i dont know haw to test them, but L2 has a resistance of 0.5ohm measured in the board, and D3 measures 3.013kohm one way, and 578ohm the other way, also in the board.

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10 months 2 weeks ago #12671 by roadrune
Replied by roadrune on topic Modular clock issue
Ok, since Q1 was cold, i tried to power up again, this time tubes and LEDs flash imediatly, VIN measured 6.6V and Q1 got hot and started smelling instantly.

At this point i am concidering a new board from a different manufacturer, i think it is to much trouble for a clock that is only about a year old.

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10 months 2 weeks ago #12672 by Ty_Eeberfest
Replied by Ty_Eeberfest on topic Modular clock issue
Those readings don't seem unreasonable. As for replacing the board, that's up to you, I have no axe to grind one way or the other. I'll just say that I have two Modulars here that have been running fine for several years. Also I'd suggest you contact Ian via email link at the store site before you decide anything.

Look into it later when the dust is clearing off the crater.

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10 months 2 weeks ago #12673 by roadrune
Replied by roadrune on topic Modular clock issue
Thanks.

Ive sent Ian an email, so i will wait for his reply before deciding.

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