Revox A77 - Backplane PCB Extender 0.15in pitch

[Mikebee88]

I’m wanting to construct a backplane PCB extender card that’s will allow me test point access to the Revox A77 plug-in PCB modules. The pitch for the edge contacts of these PCBs is 0.15in or 3.81mm. Vero still make their stripboard with that pitch and I have cut several pieces to match the size of the A77 PCBs. What I can’t seem to source is an edge connector that I would solder to the Veroboard thus making a suitable PCB extender card. RS used to list such a single sided connector with a 0.15in pitch and a range of 8, 12 and 16 ways but alas this is now no longer available. Short of cannibalising a scrap A77 switchboard I can’t think of an alternative solution! Any suggestions (or offers of a scrap A77 switchboard!) would be most welcome.

[Ted Kendall]

I wouldn;t have thought there was much in the plug-in cards that couldn't be found by cold checks - is there something in particular you're trying to fix?

[DMcMahon]

Thought I saw a couple of 0.155" hopefuls on electrojumble but their Home page says "Closed until further notice".

[TonyDuell]

A word of caution. The Americans used 0.156" edge connectors a lot and these are _NOT_ compatible with 0.15" ones in my experience. The error mounts up over the length of the connector.

[DMcMahon]

Thank you Tony, I did wonder about that.

[Mikebee88]

Thanks for all the comments so far. This need for an extender card arose out of a requirement to make checks at the contact area of the plug-in PCBs. I have a Revox A77 Mk IV which is recording only to a very low level to both channels and on playback can only just be heard with the volume control at max. I have another A77 which works perfectly and have swapped all seven PCBs from the faulty machine to this machine with no problem. The 'faulty' machine plays back known good tapes as expected and so I have to assume the fault lies elsewhere, eg the switchboard itself. When I acquired this particular A77, C307, (250mfd) had gone S/C and taken out R313, (39R), all part of the 21V rail. I replaced this along with all the other electrolytics on the switchboard. Checks on the erase and record head connections with a 'scope are as expected; modulation waveform from the playback head is only just discernable. The heads show no sign of wear and are, of course, scrupulously clean and demagnetized. If anyone has experienced anything similar I'd be pleased to hear about it!

[DMcMahon]

Hi Mike,

This sounds very difficult, if I have correctly understood all you say it seems like the record head is for whatever reason not recording a good signal on both channels.

Do you get normal/good record level signals on the VU meters ?

Have you tried to see if there is any audio signal superimposed onto the much larger record bias signals going to the record heads ? it can very very difficult see on many recorders.

David

[jamesperrett]

Does a tape recorded on your other machine play back on this one or is it quiet too?

[Amraduk]

Hello James,

Originally Posted by jamesperrett

Does a tape recorded on your other machine play back on this one or is it quiet too?

See post 6 above.

Regards,

Dave.

[TIMTAPE]

Originally Posted by Mikebee88

Thanks for all the comments so far. This need for an extender card arose out of a requirement to make checks at the contact area of the plug-in PCBs. I have a Revox A77 Mk IV which is recording only to a very low level to both channels and on playback can only just be heard with the volume control at max...

OK, the sound is very low but what is the character of the sound? clean and balanced? distorted? (re the input signal)

Is the tape intimately contacting the record head gaps as well as the play head gaps?

Have you set the machine up as per the manual? Bias, rec level etc?