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-   -   Revox PR99 Keeps Blowing Fuse (https://www.vintage-radio.net/forum/showthread.php?t=191258)

EdGizzard 18th May 2022 8:50 am

Revox PR99 Keeps Blowing Fuse
 
1 Attachment(s)
Hi All,

My RevoxPR99 started giving me problems yesterday. It was suddenly jumping out of record mode. As the day wore on it started dropping out of record and also the counter display would go out. After turning on and off it could be put into record again and was fine for the rest of the day. Got the job done :-)

Came in the morning to have a look at it and see if I could figure out what the issue. But now it will immediately blow a fuse when turned on. The fuse that blows is the empty fuse holder in the photo.

Any thoughts on what to test first would be greatly appreciated.

Many thanks
Ed

Ted Kendall 18th May 2022 11:26 am

Re: Revox PR99 Keeps Blowing Fuse
 
Could be the rectifier or smoothing on that circuit breaking down.

theredhouseinn 18th May 2022 12:39 pm

Re: Revox PR99 Keeps Blowing Fuse
 
That is the fuse for the 21v power supply to the electronics.
You have obviously got a short circuit on that line.
If you have an Avo meter check the resistance on the 21v line and fault find from there.
Suspect are the Fraco's and riva's caps. Ckeck the suppression cap across the mains input supply, it is behind the panel with the mains socket and fuse holder on it. If it has not been changed, it will blow eventually, and blow the mains fuse.
John.

Michael Maurice 18th May 2022 4:23 pm

Re: Revox PR99 Keeps Blowing Fuse
 
I have had the bridge rectifiers fail on these recorders. You have to remove the power transformer to get to it.

I suggest you also replaced the two 2200uF capacitors on the power board.

Whilst you are working on the machine, replace the Rifa capacitors, one on the capstan control board, the other across the mains (Located on the panel where the mains input socket and the fuse holder are located.

EdGizzard 18th May 2022 5:25 pm

Re: Revox PR99 Keeps Blowing Fuse
 
Thanks Guys!! Fantastic advise.

Going to spend a day on it this week. I'll report back

Thanks again

EdGizzard 19th May 2022 12:12 pm

Re: Revox PR99 Keeps Blowing Fuse
 
Hi All,

I believe the problem is the rectifier connected to the fuse in question.

The test results below are taken with the rectifier still soldered to the PCB. MM in diode mode.

With + probe of MM on - of rectifier:

- to AC pin 1 - 001
- to AC pin 2 - 663

With - probe of MM on + of rectifier:

+ to AC 1 pin 1 - 663
+ to AC 2 pin 2 - 636

Same test on the other rectifier gives readings of around 650 throughout.

Markings on the original Rectifier are KBPC1-01 204. I was going to replace them with these. what do you think:

https://uk.rs-online.com/web/p/bridg...ifiers/7005478

For the two capacitors:

https://uk.rs-online.com/web/p/alumi...citors/1084992

Any thoughts on a good replacement for the RIFA cap? (0.47 uf150v 60Hz)

I tested the 3 caps behind the mains cable socket and they all appear ok.

Thanks so much guys.

Ed

Restoration73 19th May 2022 12:45 pm

Re: Revox PR99 Keeps Blowing Fuse
 
In 2000, I bought an ex broadcast PR99MK3 for 500 - a bargain, I thought.

It worked fine the first time powered up, but the second time the fuse blew - yes it was
the bridge. I was able to replace it with the pcb in situ - I used a 200V version.
I would use a 105 degree type for the capacitor though rather than the 85 degree shown.

EdGizzard 19th May 2022 2:03 pm

Re: Revox PR99 Keeps Blowing Fuse
 
Dont think RS do a 200v version. Keen to use RS as i can get the parts by tomorrow. Have an account.

So was thinking of ordering these today:

https://uk.rs-online.com/web/p/bridg...ifiers/7005478

and

https://uk.rs-online.com/web/p/alumi...citors/7111510

Do you think they will suffice?

Thanks guys

Michael Maurice 20th May 2022 6:49 pm

Re: Revox PR99 Keeps Blowing Fuse
 
I use these capacitors in the power supply. Far better than Jackson capacitors IMHO

DMcMahon 21st May 2022 7:11 am

Re: Revox PR99 Keeps Blowing Fuse
 
Quote:

Originally Posted by EdGizzard (Post 1471596)
Dont think RS do a 200v version. Keen to use RS as i can get the parts by tomorrow. Have an account.

So was thinking of ordering these today:

https://uk.rs-online.com/web/p/bridg...ifiers/7005478

and

https://uk.rs-online.com/web/p/alumi...citors/7111510

Do you think they will suffice?

Thanks guys

Looking at the MK. II schematics, the bridge rectifier for the +21V supply (D2) appears to be identified as 35V/2A, so your RS item will be fine.

David

EdGizzard 27th May 2022 2:30 pm

Re: Revox PR99 Keeps Blowing Fuse
 
!!!!PR99 WORKING!!!!

Thanks so much everyone. Hardest part was getting the PCB out so I could change the components. :-)

Ed


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