I was reading through a thread in the archives about capacitor problems in power supplies. Other than not turning on, can anyone shed some light on symptoms? Specifically state of the internal power LEDs.

My E8285A won't power up. NONE of the internal power LEDs are on... +5V, +12V, -12V, +12VSTBY are all OFF. The last time I successfully used it, it had problems powering up. It got part way through the boot sequence, hung for a short time, reverted to the beginning on its own and then successfully came up and seemed to be working OK. Next time I tried to power it up, it was completely dead.

I am wondering if bad capacitors in the power supply might be the problem when all of the LEDs are off? I don't think I can troubleshoot this supply, but I could try replacing all of the capacitors. If I do that, should I replace caps in on the regulator board too?

Paul N1BUG

I have read about that vertical board. There are five small vertical boards on the main power supply board of the 8285 but I don't know if any of them is the equivalent. I was thinking of recapping the whole power supply but it looks like I am going to have trouble finding capacitors with the right physical size and lead spacing.

Paul N1BUG

I've got an 8921 (analog cellular and lmr) that had similar issues. I noticed it began to take longer to start. Push the switch and nothing happens for a while, then it started up and ran fine. It got so it would take 5 min or so before anything happened.? I pulled the supply out and replaced all the electrolytics.? That was my issue.

I then measured the esr on all the caps and only one was bad, a 33u 50V. As I recall it was on or at least near the small vertical board. If you go to all the effort to pull the supply, I'd replace all the caps. It's not too $$ or time consuming.

Be aware the fan rpm sensors are used in E8285A. If a fault exists in fan/s, the PSU will not turn on.
Only 2 out of 5 E8285A power supplies I have repaired worked by simple recapping. I never managed to get 2 working. The other had issues with the HV rail - think its 40V? Cant recall - though I do remember the voltage is required for PIN diodes in various PLLs and often the cause of OOL LEDS coming on. Anyway I replaced all parts in the HV supply to get it going. Most modern caps are smaller - make sure you use 105Deg C caps.

I have read in the group archive some recommendations to replace all the caps. I have already pulled the supply and have the main board here on the bench. I have been able to read the value on all but one cap (oriented such that I can't see it) and am trying to find replacements that have the correct lead spacing and are small enough to fit. With ongoing supply chain problems, now is a bad time to be doing this.

Paul N1BUG

Thanks. If you only fixed 2 of 5 with caps that doesn't sound very promising. I assume the +12V STBY LED should at least be on? Mine isn't, so I'm guessing that means at least one problem with the power supply. I have lost much of my bench capability without this instrument but it's starting to look like I should put it back together and forget it until we have fewer supply issues at the very least. I am not finding replacements for some of these caps that will fit in the available space and have correct lead spacing.

Paul N1BUG

开云体育

Hello, .

Sunday, January 30, 2022, 0:31:03, Sgc1823 wrote:

I've got an 8921 (analog cellular and lmr) that had similar issues. I noticed it began to take longer to start. Push the switch and nothing happens for a while, then it started up and ran fine. It got so it would take 5 min or so before anything happened. ?I pulled the supply out and replaced all the electrolytics. ?That was my issue.

If you ordered caps from Digikey or some other major distributor - can you share part numbers you ordered from order history? It would be great help to anyone who try to find a set of right caps for their dying 892x.

Regards,
Yuri.


--
Best regards,
Yuri ? ? ? ? ? ? ? ? ? ? ? ? ?mailto:yuri@...

Hank and group,

I am back to it after a day and a half digging out from the blizzard.

I've spent the last several hours working on this. After correcting a couple of mistakes on lead spacing I am stuck on just a couple of caps now.

The infamous 10uF tantalum cap. I cannot read the voltage on the original part but since it is in a 40V circuit I assume 50V. Original is axial, approx 4.5mm D x 9mm L. Closest I can find is 13.46mm L. This will not fit without standing on end with one long lead or (maybe) folding both leads under the part.

My only choice for 33uF 25V, approx 5mm D x 5mm H, 2.5 LS seems to be a slightly larger NTE part offered through Digi-Key Marketplace.

I don't know if lead lengths are critical in this power supply but past experience with switching circuits at 137 kHz tells me it can matter at low frequencies. I am trying to stick with parts that fit as the originals.

This power supply board has had 3 FETs replaced before. Whoever was in here last failed to put thermal paste between the L shaped heat sinks the devices are mounted to and the heat sink plate that mounts to them. Pictures of other E8285As I have seen had thermal paste there.

Paul N1BUG

Just posting an update for the archives...

I replaced 29 capacitors on the power supply board: 28 electrolytic and one tantalum. Also replaced primary and secondary memory backup batteries as preventive maintenance.

On the first boot it came up error code 0040 on the self diagnostics. The service manual says that is Real-Time Clock failure, Memory board. The error appeared just the one time. It has come up all self tests passed on subsequent boots. I will assume that was just some clock confusion due to replacing the memory battery. I didn't even know it had a real time clock but will look into that.

All functions seem to be working normally.

73,
Paul N1BUG

Paul,

Great news.? I thought there would be a happy ending to this story.

I've been meaning to ask you what has been going on with the few replacement caps you'd said weren't too good of a fit.

Thanks for the update which is very important to do.? Although quite complete, I do have some questions for you.? Maybe later today or tomorrow for those.

Hank

Hank,

A few additional comments that may be of interest to others:

Digi-Key was the only major vendor that could supply the parts at this time.

I was able to stick with 105C on all electrolytics, but some were 1000 hour rated life. I would normally buy longer life caps if I had that option. This may be related to ongoing supply chain problems. Longer life caps were listed as out of stock.

The NTE 33 uf caps 6.5 x 6.5 mm fit OK in place of the slightly smaller original parts. The four of those are on the small vertical boards. Those were ordered through Digi-Key Marketplace and shipped directly from NTE Electronics. There was an additional steep shipping charge and it took an extra week.

Only one part required special mounting. The body of the axial tantalum cap was longer than the hole spacing on the board. I mounted it at a 45 degree angle with the positive end up, which resulted in about half inch lead length on that end.

I will do my best to answer any questions.

Paul