开云体育

Hi all.

Can't seem to find these anywhere.

According to Sphere, these are,

'HARD to find 49xP Series Inverter Transistors! - 2N6587, TO-61, NPN, 10A/450V' - (SOLD OUT)

Is these a feasible request, or shall the 492 be stripped and sold for spares?


James

An NPN is an NPN is an NPN, no?
Therefore, it must be possible to use a more common package of transistor and bodge a solution to this unobtainium nonsense?

Ok, we don't know the Gain, but we do know it is 10A and 450v and I'm sure I can figure out which terminals are the B,C & E.

This TO-61 package is the 'bolt and nut' type and was attached to a fat heatsink, so why can't a couple of different NPN's be used instead? Maybe TO-247's laid flat on the heatsink instead of passing through it?

Surely this has been done before?

Unless of course these chips aren't 'normal'...

James,

A BUV48A will work and is heavier capacity. Mouser has these in stock for $6,76.

Mark

Thank you Mark.

I can actually source these locally.

Looking at the board, the pin layout isn't as obvious as I thought and I haven't been able to find any kind of schematic for the 492 PSU so I'll just assume that the TO-61 pinout is standard to all TO-61's.

James

Hi James,
The PSU schematic is f.i. at pdf page 225 492/492P Spectrum Analyzer Volume 2 Service manual ( 070-3784-01Tekwiki).
Albert

Hi Albert.

If I was fairly confident that I had the correct pin-out, you've made me certain.

Many thanks

Quick progress report;

..is that with the unit open on the bench, and with two 2SC4430's (the BUV48A's were overpriced in the shop) in place of the 151-0703-00's then the voltage rails are once again working. So that's great news!

Thanks to Mark and Albert for their help.

The only thing that stands out, is that the little neon next to the two large filter caps is lightly flickering away. I never had the unit open before but aren't those neons for circuit protection in the event of a fault?

James



It's late here now but tomorrow I'll assemble everything

James,

The neons are there to help discharge the condensers when it is turned off. When on, the limiting resistor makes the combination of the R and Ne a relaxation oscillator. These blinking when on is normal operation.

Mark

In that case... Excellent!

This thing was picked up very cheap at the flea market and have no idea as to it's history, however it does seem to be complete, so let's see what happens with the PSU working?

Thanks again.


James

So,
reassembled and turned on, the unit fires up, or at least all lights and scale illumination light up, before leaving three led's and the scale illumination on, but nothing else. No response to anything.

Checking the voltage rails at the test points near the front left reveal that all are fine except the -15v which reads -1.5v

Honestly not sure about how much time to devote to this, although perhaps it's something as simple as bad electrolytics or tantalums?

Picked up a nice, functioning 7633 with the 7L13 Spectrum Analyzer plug-in for less than 10 British Pounds, so perhaps I should just pass this 492 along?

If anyone has any suggestions, please feel free...


James

Hi James
Always interested in a repair project - am in Cheshire - so if you decide to part with the 492 then please let me know

Best regards

Dominic

Hi Dominic.

I'm in Brazil, and this this weighs more than the plane needed to fly it across the Atlantic.

Good luck though with your projects.

James

If anyone is interested, just an update to say that the -15v problem is located on the A62 Video Amplifier board.

With that board removed the CRT and controls come back to life with crisp details.


Have to go to work now but shall see if it can't be fixed later.

Progress!

:)

Hi chaps.

I suppose this is the final update, as found a shorted 47?F 20v cap (C6033) on the A62 board, and now the 492 appears to be working again (although I don't yet know how to use it, to be sure).

Anyway... Fantastic!

Must finally be getting somewhere with my 'diagnose and repair' abilities. Lol...


Thanks again to Mark and Albert, as after looking at the complexity of the instrument, I was honestly not gonna follow this through.


James