Philips DCC951 scorching power supply and dimly lit display

Hello. I own a philips DCC951 just purchased on ebay. I have a dimly lit display, the pinch rollers to replace (I found them here on the dcc museum) and the cooling fin of the 60 degree celsius power supply. The electronic part seems to be working properly, for what I can hear with the deformed pinch roller. But 60 degrees celsius seems too much to me.
What about the display? anyone know it is possible to increase the brightness or should I replace it?
Anyone have any suggestions?
Thank you and greetings. Umberto

Very likely a dim VFD display is caused by a weak negative power supply. I don’t have the schematics handy at this time but I bet there’s a power rail that only goes to the display and is something like -30V or -70V or something. Check the voltage (be careful) and replace the capacitors in the section of the power supply that generate that voltage.

===Jac

2 Likes

Thanks JAC, I will check the -30V supply branch. For the high temperature of the final transistors of + 10 / -10 Volt do you have any suggestions? The presence of 800mA fuses on the two branches excludes an anomalous current absorption. Maybe some element shorted before the fuse? Thanks Umberto

Nothing in front of the fuses will cause excessive current through any of the circuitry that’s protected by those fuses, of course.

In theory, if the input voltage for the power regulators is too high, the regulators will dissipate more current to keep the output voltage the same. That could cause more heat than normal. But I can’t really think of why there would be an over-voltage, unless your unit has the wrong transformer for your mains voltage (120V transformer on a 230V mains) or there’s something wrong with the transformer itself (very unlikely: the most common (but very unlikely) failure in a transformer is a short in the windings but that would cause a DROP in voltage).

By far the most likely (electronic) failure in the entire unit is capacitors. A failed/failing filter capacitor just behind the regulator could be (partially) shorted and cause excess current, resulting in extra heat produced by the regulator. But the fuses will protect things from a real short circuit.

Check the voltages in the power supply against the service manual and see if they’re okay.

It might be that everything is just okay, by the way. I don’t know how hot your recorder would normally be but it has no ventilation inside and DCC recorders use linear (not switched) power regulators so there is some heat build up. As long as the outside stays under 45 C / 113 F, I wouldn’t worry about it.

=== Jac

Hi Jac, I have just finished measuring the voltages on the power supply and they are all correct, including the -32V of the display VFD. The capacitors are ELNAC but have their years and therefore I will replace them. The display may simply be out of stock, but finding it a replacement I think is impossible. Thanks for your patience, I continue to investigate while I wait for the pinch roller to arrive. Umberto

Maybe @drdcc has a donor of one otherwise dead unit.

I will check and contact Umberto.

1 Like

Maybe! You could do a single shipment together with the pinch roller.

We have a display available. Just send you a message via mail.
Ralf

1 Like

I replied privately to drdcc@dccmuseum.com. I await the shipment of everything. Which carrier will you use?
Thanks Umberto

Usps

Thank’s I’m waiting. Let me know.
Umberto